Kiki Bertens

2.1. 2009-2015: Early career and first WTA Tour title

Bertens turned professional in 2009. She began the 2012 season attempting to qualify for the 2012 Australian Open, where she advanced to the second qualifying round before a thigh injury forced her to retire from a subsequent tournament in Andrézieux-Bouthéon. She represented the Netherlands in the 2012 Fed Cup, contributing to wins against Portugal and Estonia. In February, she competed in the qualifiers for the Acapulco WTA tournament, reaching the second round.

Her early success on the ITF Women's Circuit included winning her second ITF singles title in Irapuato, Mexico, by defeating Yaroslava Shvedova. She continued this form by winning another ITF title in Bath, overcoming Annika Beck in a three-set final.

In April 2012, Bertens made her breakthrough at the WTA Tour event in Fès, Morocco. Entering as a qualifier, she won her first main-draw WTA singles match and remarkably went on to reach the final, defeating notable players such as Urszula Radwańska, Garbiñe Muguruza, and Simona Halep. In the final, she defeated Laura Pous Tió 7-5, 6-0, securing her first WTA singles title. This achievement made her the first Dutch female player since Michaëlla Krajicek in 2006 to win a WTA singles tournament.

She made her Grand Slam main-draw debut at the 2012 French Open after successfully qualifying, but lost in the first round to Christina McHale. At Wimbledon, she secured her first Grand Slam win by defeating 19th seed Lucie Šafářová in the first round, before losing in the second round. After a brief period of early exits, Bertens regained form during the American hardcourt circuit, qualifying for events in Montreal and Cincinnati, and notably upsetting former world No. 3 Nadia Petrova in Montreal. At the 2012 US Open, she avenged her French Open loss by defeating Christina McHale in the first round. She ended her 2012 season with a quarterfinal appearance at the WTA tournament in Seoul before fatigue led to early exits in subsequent events.

Starting 2013 ranked world No. 63, Bertens reached the quarterfinals of the Auckland Open, defeating Svetlana Kuznetsova and Heather Watson. She continued her good form at the Paris indoor event, entering as a lucky loser and reaching the semifinals before retiring due to a back injury against top seed Sara Errani. At the 2014 French Open, she reached the fourth round as a qualifier, marking her best Grand Slam performance at that point, though she was defeated by Andrea Petkovic. In 2015, she changed coaches from Christiaan de Jong to Raemon Sluiter.

2.2. 2016-2017: Grand Slam breakthrough and two WTA titles

The 2016 season marked a significant turning point in Bertens' career. After early losses in Auckland, Hobart, and the Australian Open, she delivered crucial performances in the Fed Cup tie against Russia, defeating Ekaterina Makarova and Svetlana Kuznetsova, leading the Netherlands to an upset victory. She continued her Fed Cup winning streak against France in the semifinals, beating Caroline Garcia and Kristina Mladenovic, though the Netherlands ultimately lost the tie in the deciding doubles match.

On the clay courts, Bertens reached the semifinals in Rabat. At the Nuremberg tournament, she won her second WTA singles title, her first since 2012, by defeating Mariana Duque Mariño in the final. This included her first career win against a top-10 player, Roberta Vinci. She also won the doubles title in Nuremberg alongside Johanna Larsson.

Her most notable achievement of the year came at the 2016 French Open. She upset third seed Angelique Kerber in the first round and continued her impressive run, defeating Camila Giorgi, Daria Kasatkina, Madison Keys, and eighth seed Timea Bacsinszky to reach her first Grand Slam semifinal. In the semifinal, despite suffering from a left calf injury and holding two set points in both sets, she lost in straight sets to top seed Serena Williams. This remarkable performance propelled her into the top 30 of the WTA rankings for the first time.

Following her French Open success, Bertens reached the third round of Wimbledon before losing to Simona Halep. She reached the final of the inaugural Ladies Championship Gstaad but lost to Viktorija Golubic. Despite winning her second singles title and reaching a major semifinal, the latter part of 2016 saw a string of six consecutive first-round losses, including at the Rio Olympics and 2016 US Open. She rebounded by winning two more doubles titles with Johanna Larsson in Linz and Luxembourg, and reached the singles semifinals in Luxembourg. She concluded her season at the 2016 WTA Elite Trophy, losing both of her group matches.

Bertens began 2017 by winning the doubles title in Auckland with Johanna Larsson, but struggled in singles, experiencing early exits at the Australian Open and other tournaments. She gained momentum during the clay-court season, reaching the quarterfinals of the 2017 Mutua Madrid Open and the semifinals of the 2017 Italian Open. She successfully defended her title at the Nuremberg tournament, securing her third career singles title. Despite a strong clay season, her French Open campaign ended in the second round, and she faced early exits at Wimbledon and other grass-court events.

She rebounded again at Gstaad, where she won both the singles title (her fourth) and the doubles title with Larsson. The North American hardcourt swing proved challenging with early losses, including a first-round exit at the 2017 US Open. Bertens finished the 2017 season strong in doubles, reaching her biggest career final at the WTA Finals with Johanna Larsson, where they ultimately lost to Tímea Babos and Andrea Hlaváčková. She finished the year ranked 31st in singles and achieved a new career-high of 19th in doubles.

2.3. 2018: Top 10 debut and Premier titles

The 2018 season was a pivotal year, seeing Bertens' ascent to the top 10. She started by winning the doubles title at the 2018 Brisbane International with fellow Dutch player Demi Schuurs. After reaching the third round of the 2018 Australian Open (losing to eventual champion Caroline Wozniacki), she achieved a significant milestone in April by winning her first Premier title at the Charleston Open, defeating Julia Görges in the final.

At the 2018 Mutua Madrid Open, Bertens had an exceptional run, defeating world No. 2 Caroline Wozniacki and Maria Sharapova en route to her first Premier Mandatory final. Although she lost to Petra Kvitová in a closely contested final, her performance showcased her growing prowess on clay. She reached the quarterfinals of Wimbledon, a career best at the event, with impressive wins over nine-time champion Venus Williams and seventh seed Karolína Plíšková, before falling to Julia Görges.

The North American hardcourt swing brought further triumphs. At the Canadian Open in Montreal, she defeated two top-10 players, Karolína Plíšková and Petra Kvitová, to reach the quarterfinals. The following week, she captured the biggest title of her career at the Cincinnati Open, defeating four top-10 players-Wozniacki, Elina Svitolina, Kvitová, and world No. 1 Simona Halep-in a challenging draw. In September, she secured her second hardcourt title at the Korea Open, overcoming Ajla Tomljanović in the final.

Her consistent high-level play led to her first qualification for the 2018 WTA Finals, where she reached the semifinals before losing to eventual champion Elina Svitolina. In recognition of her remarkable improvements and ascent, Kiki Bertens was named the "Most Improved Player of the Year" by the WTA in October 2018. She finished the year ranked world No. 9, marking her debut in the top 10.

2.4. 2019: Career-high ranking and Premier Mandatory title

Bertens continued her strong form into 2019, starting with a semifinal appearance at the 2019 Sydney International. In February, she won her first title of the year at the 2019 St. Petersburg Ladies' Trophy, defeating Donna Vekić in the final. She reached the fourth round at both Indian Wells and the 2019 Miami Open, losing to eventual champion Ashleigh Barty in Miami.

Her clay-court season was highlighted by her triumphant victory at the 2019 Mutua Madrid Open. After cruising through her early matches, she avenged her 2018 final loss to Petra Kvitová in the quarterfinals and defeated Sloane Stephens in the semifinals. In the final, she beat world No. 3 Simona Halep in straight sets, becoming the first player to win the Madrid Open without dropping a set, and her first Premier Mandatory title. This historic win propelled her to a new career-high ranking of world No. 4 on 13 May 2019. She followed this with a semifinal appearance at the 2019 Italian Open, where she notably defeated world No. 1 Naomi Osaka, before retiring due to illness in the second round of the 2019 French Open.

On grass, she reached the final of the 's-Hertogenbosch and the semifinals of Eastbourne. Her US Open Series saw early exits in Toronto and Cincinnati, but she reached the third round of the 2019 US Open. In the Asian swing, she reached the semifinals of the 2019 China Open after defeating multiple strong opponents, including Elina Svitolina, before losing to Ashleigh Barty. She concluded her season by reaching the final of the 2019 WTA Elite Trophy, losing to Aryna Sabalenka, and also participated as an alternate in the 2019 WTA Finals, where she defeated world No. 1 Ashleigh Barty before retiring due to injury. She ended the year ranked No. 9. On 1 November 2019, she announced that Elise Tamaëla, her interim coach, would officially take over from Raemon Sluiter.

2.5. 2020-2021: Injuries, loss of form, and retirement

The 2020 season started positively for Bertens. She reached the semifinals of the 2020 Brisbane International and the fourth round of the 2020 Australian Open (losing to eventual runner-up Garbiñe Muguruza). She then successfully defended her title at the 2020 St. Petersburg Ladies' Trophy, defeating Elena Rybakina in the final to secure her tenth and final WTA singles title. This was her last tournament before the WTA Tour was suspended due to the COVID-19 pandemic.

Upon the tour's resumption, Bertens chose to skip the US Open. Her return at the 2020 Italian Open and Strasbourg saw early losses. At the 2020 French Open, she reached the fourth round in a controversial second-round match against Sara Errani, which saw Bertens leave the court in a wheelchair due to cramping, leading Errani to accuse her of faking injury. Bertens then lost to Martina Trevisan in the fourth round. The following month, she announced she would undergo Achilles tendon surgery, effectively ending her season. Despite the injury setback, she finished 2020 ranked world No. 9 for the second consecutive year.

The 2021 season was significantly impacted by her Achilles tendon surgery. She missed the start of the year and struggled upon her return, suffering first and second-round losses in her initial tournaments in Qatar, Dubai, and Miami. In May, as the defending champion at the 2021 Mutua Madrid Open, she was defeated in the second round, causing her ranking to drop to No. 17. A first-round loss at the 2021 French Open further saw her ranking fall out of the top 20 for the first time since June 2018.

On 16 June 2021, Bertens announced that 2021 would be her final season, citing her inability to compete at the highest level due to persistent injuries. She stated she would retire after the 2020 Summer Olympics or by the end of the season. She subsequently experienced first-round exits at Eastbourne and Wimbledon. Her professional career officially concluded at the Tokyo Olympics. She lost in the first round of the singles draw to eventual silver medalist Markéta Vondroušová. Her final match was in the doubles draw, partnering Demi Schuurs, where they lost in the second round. Bertens retired from the tour ranked world No. 24 in singles and No. 112 in doubles.

5.1. WTA Tour Finals

Bertens competed in several WTA Tour finals in both singles and doubles, achieving a notable number of titles and runner-up finishes.

5.2. Grand Slam Performance Timelines

Kiki Bertens' year-by-year performance at the four Grand Slam tournaments is detailed below.