Williams began the 2015 season by representing the United States alongside John Isner at the Hopman Cup. The American pair lost the final to the Poland. At the Australian Open Williams defeated Maria Sharapova for the 16th consecutive time to claim her 6th Australian Open singles title and 19th career Grand Slam singles title, winning the title on her third match point in the second set. With this victory Williams surpassed both, Evert and Navratilova, for second most Grand Slam singles titles won in the Open Era. The title was also her sixth Grand Slam singles title since turning 30 years of age, three more than the next closest to do so (Margaret Court, Martina Navratilova with three each). She is the only player in history to win all four Grand Slams at least once after having turned 30. The following weekend, Serena and sister Venus traveled to Buenos Aires to face Argentina in a World Group II tie for Fed Cup. She played and won her only match against María Irigoyen to help Team USA to a 4–1 win over Argentina. Williams announced that she would be competing at the Indian Wells Masters ending her 14-year boycott of the event. Upon her return Williams received a standing ovation from the crowd and won her first match in straight sets. She reached the semifinals, where she was due to face No. 3, Simona Halep, for a place in the final, but was forced to withdraw because of a knee injury. By virtue of having defeated Sabine Lisicki in the quarterfinals of the Miami Open, Williams became only the eighth woman in the Open Era to record 700 match wins in her career. This also made her one of only three active players to have won 700 or more matches in singles, others being Roger Federer and Rafael Nadal. In the semifinals she won against Halep to advance to her tenth final at the event where she won a record eighth title and extended her winning streak to 21 by beating Carla Suárez Navarro.