WIMBLEDON, England—Despite many recent three-set victories, Serena Williams says she still gets nervous in deciding sets. At the Grand Slams this year, Serena has won all nine three-set matches she's played.

To reach the semifinals of Wimbledon, Williams was pushed to three sets by both Heather Watson and Victoria Azarenka.

“I feel really vulnerable in a third set, if I'm down a set,” Williams said. “I just feel this is another opportunity for me to lose. I have one more set to win or to lose. I just go for it. At that point I kind of relax and see whatever happens, happens.”

Williams will face Maria Sharapova in the semifinals; she leads the Russian 17-2 in head-to-head matches. Sharapova upset Williams in the 2004 Wimbledon final and later that year beat her again at the WTA Finals in Los Angeles. Since then, Williams has beaten Sharapova 16 matches in a row, including the round of 16 at Wimbledon in 2010. Williams also defeated Sharapova in the final of the 2012 London Olympics, held at the All England Club, 6-0, 6-1.

Williams has won their past five meetings in straight sets, including the 2015 Australian Open final, 6-3, 7-6 (5).

“I love playing Maria. I think she brings out the best in me,” Serena said. “I think I bring out the best in her. I thought we had a wonderful final in Australia. It was very entertaining. She played really well. For me, I don't feel like I have any pressure going into this match. We both actually lost early last year. We both are kind of enjoying this moment and one of us will be in the final.”