加比涅·穆古魯薩

Muguruza reached her second major quarterfinal at the 2015 French Open.

Muguruza's first event of the year was to be the Brisbane International but she was forced to withdraw from the event due to an ankle injury.[3] The following week, Muguruza chose not to defend her title at the Hobart International and competed at the Sydney International instead, where she reached the quarterfinals, defeating Agnieszka Radwańska for the first time in her career en route.[4] At the Australian Open, she progressed to the fourth round for the second consecutive year with wins over Marina Erakovic, Daniela Hantuchová and Timea Bacsinszky before falling to the eventual champion, Serena Williams in three sets.

Muguruza won both of her singles rubbers in the 2015 Fed Cup World Group II, defeating Irina-Camelia Begu and world No. 3 Simona Halep but Spain lost the tie 3–2 after Muguruza and her compatriot, Anabel Medina Garrigues lost the deciding doubles rubber. At the Dubai Tennis Championships, Muguruza reached her first WTA Premier 5 semi-final in singles, defeating qualifier Jarmila Gajdošová, twelfth seed Jelena Janković, fifth seed Agnieszka Radwańska and thirteenth seed and doubles partner Carla Suárez Navarro before falling to the seventeenth seed and eventual runner-up, Karolína Plíšková in three sets. She also reached the final of the doubles with Suárez Navarro. The following week, Muguruza retired from her first round match against Suárez Navarro at the Qatar Open while trailing 6–5 in the first set.

In March, Muguruza lost to Ka. Plíšková in the third round of the Indian Wells Masters after a second round win over American wildcard Irina Falconi. Despite this, she rose to a career high singles ranking of world No. 19 after the event. A fortnight later, Muguruza reached the third round of the Miami Open after defeating qualifier Sesil Karatantcheva but lost to the eleventh seed Sara Errani after winning the first set.

Muguruza reached the second round of the three clay court events that she competed in leading into the French Open. She lost to second seed Simona Halep in Stuttgart, Kristina Mladenovic in Marrakech and the eventual finalist Svetlana Kuznetsova in Madrid. Muguruza and Suárez Navarro also reached the doubles final of the latter for the second consecutive year but the pair lost in three sets to Casey Dellacqua and Yaroslava Shvedova. Despite failing to win back-to-back matches since February, Muguruza reached her second consecutive French Open quarterfinal, defeating Angelique Kerber[5] and Flavia Pennetta[6] en route, before losing to the eventual runner-up, Lucie Šafářová.[7]

Muguruza made a poor start to the grass court season, losing in the first round of the Birmingham Classic and the third round of the Eastbourne International after a first round bye. However, she and Suárez Navarro won their first grass court doubles title in Birmingham, defeating Andrea Hlaváčková and Lucie Hradecká in straight sets in the final. At the Wimbledon Championships, Muguruza defeated 10th seed Kerber in the third round,[10] 5th seed Caroline Wozniacki in the fourth round,[11] 15th seed Timea Bacsinszky in the quarterfinals and 13th seed Agnieszka Radwańska in the semi-finals to advance to her maiden Grand Slam final. She played against world No. 1 Serena Williams for the title, but lost in straight sets.[12] After the tournament, Muguruza entered the Top 10 for the first time, moving up to world No. 9 in the WTA Rankings.

During the US Open series, Muguruza did not enjoy much success, dropping her opening matches in Toronto and Cincinnati to qualifiers Lesia Tsurenko and Yaroslava Shvedova respectively. At the US Open, she recorded her first win at the tournament by defeating German Carina Witthöft in the first round. However, she fell short to Johanna Konta in the following round in three sets, the match was a total time of 3 hours and 23 minutes, the longest women's singles match in that tournament's history since the introduction of tiebreaker in 1970.

Muguruza kicked off the Asian swing at the Pan Pacific Open where she successfully advanced to the last eight after defeating Barbora Strýcová before losing to eventual finalist Belinda Bencic in straight sets. At the Wuhan Open, Muguruza successfully cruised into her second straight quarterfinal at the event after dispatching Sloane Stephens and Ana Ivanovic. She then went on to defeat the likes of Anna Karolina Schmiedlova and Kerber to reach the final where she faced Venus Williams but was forced to retire in the second set with an ankle injury. Muguruza was able to crack the Top 5 for the first time in her career after the tournament's conclusion.[13] At the China Open, Muguruza breezed by Irina Falconi before going the distance against Mirjana Lučić-Baroni to advance to the quarterfinals. With the win, Muguruza qualified for the WTA Finals for the first time. She will be the first Spaniard to compete at the year-end championships since Arantxa Sánchez Vicario in 2001. She then beat Bethanie Mattek-Sands and Radwańska to advance to her maiden Premier Mandatory final. With her semifinal win over Radwańska, Muguruza cracked the Top 4 rankings where she reached a career high of world No. 4. She went on to defeat Bacsinszky in straight sets to claim her first Premier Mandatory title and her biggest title of her career.

Muguruza then traveled to Singapore for the WTA Finals, where she went undefeated in the round robin play; beating Petra Kvitová, Angelique Kerber, and Lucie Šafářová. She then lost to eventual champion Agnieszka Radwańska in the semifinals. Muguruza also competed in doubles in Singapore, where she and her compatriot Carla Suárez Navarro reached the final. However, they lost to the number one seeds Martina Hingis and Sania Mirza.

Muguruza started the season at the Brisbane International, being the no. 4 seed. She made a run to the quarterfinals after three-set wins over Sam Stosur and Daria Kasatkina, and a straight sets win over Svetlana Kuznetsova. She then retired in the first set of her semifinal match against Alizé Cornet due to injury. At the Australian Open, Muguruza beat Marina Erakovic, Samantha Crawford, Anastasija Sevastova and Sorana Cîrstea en route to her first ever quarterfinal at the tournament. She then lost to Coco Vandeweghe in straight sets.

Muguruza then played the Fed Cup quarter-finals, where she beat Barbora Strycova in three sets before losing to Karolina Pliskova. Spain ended up losing the tie 2-3. During the Gulf Swing, she beat Cagla Buyukakcay in Doha, before succumbing to Zhang Shuai in three sets. She then retired in her first match at Dubai against Kateryna Bondarenko, due to injury. At Indian Wells, Muguruza advanced to the quarterfinals, beating Kirsten Flipkens, 17-year-old Kayla Day, and Elina Svitolina en route. She then lost to world no.3 Karolina Pliskova in two tiebreaks.