KEY BISCAYNE, Fla. (AP) -- Between points, Serena Williams stood motionless behind the baseline with her back to the net, as if trying to match - or mimic - the methodical ritual of her opponent, Maria Sharapova.
They took turns waiting on each other, the pace of play plodding, which only delayed the inevitable. Williams beat Sharapova for the 15th consecutive time Thursday, rallying in both sets to win 6-4, 6-3 in the Sony Open semifinals.
''I have always felt when I'm playing at my best, then it's hard for people to beat me,'' Williams said.
Rafael Nadal could say the same. He advanced to the semifinals by hitting a flurry of forehand winners down the stretch to beat Milos Raonic 4-6, 6-2, 6-4.
On Saturday, the No. 1-ranked Williams will try for a record seventh Key Biscayne title against No. 2 Li Na, who overcame 40 unforced errors to beat Dominika Cibulkova 7-5, 2-6, 6-3. Williams is 10-1 against Li.
Williams improved to 16-2 against Sharapova, whose most recent victory in their rivalry came in 2004.
''Despite my results against her, I still look forward to playing against her because you learn so much from that type of level which she produces,'' Sharapova said. ''You finish the match, and you know where you need to improve and the things that you need to work on.''
Williams can credit a superior serve and better returns for her latest win. She hit nine aces and broke five times, which helped her rebound from deficits of 4-1 in the first set and 2-0 in the second.
''I wasn't playing my best,'' Williams said. ''I knew if I wanted to stay in the tournament and make another final, I just had to play better.''
She did, earning her 14th consecutive victory against a top-10 player.
The No. 1-ranked Nadal, who is 0-3 in Key Biscayne finals, needs one more win to get there again. His opponent Friday night will be No. 7-seeded Tomas Berdych, who advanced by beating No. 22 Alexandr Dolgopolov 6-4, 7-6 (3).
Nadal has beaten Berdych 16 times in a row over the past seven years.
''This tournament is a tournament where I really feel the love of the people so much,'' Nadal said, ''so I'm going to try my best to keep playing well.''
Three-time champion Novak Djokovic will play in the other semifinal Friday against No. 20-seeded Kei Nishikori, who eliminated Roger Federer on Wednesday.
Williams first won Key Biscayne in 2002 and is the defending champion. A minority owner in the Miami Dolphins, she has worn the team's orange and turquoise throughout the tournament she considers her home event because she lives 90 minutes up Interstate 95.
''When I grew up I always wanted to play here,'' she said. ''I guess I just don't want to let go. It's my favorite stop on the tour. It's home. All my friends come. So it's perfect for me.''
There was no evidence of a home-court advantage at the start, when Williams failed to convert four early break-point chances and fell behind. Sharapova cracked a succession of winners from the baseline and earned applause from Williams after besting her in one exchange.
While Sharapova is notorious for her deliberate routine between points, Williams doesn't usually play so slowly.
''I just made some errors, and when that happened, I was just trying to regroup and get my mind back together and just try to get back focused and just try to get things going again,'' she said. ''It just helps me to be able to relax. Sometimes I do get a little uptight.''
The approach worked. Williams broke back when Sharapova committed three consecutive backhand errors, and gained momentum from there, sweeping the final five games of the first set.
The story was similar in the second set, and after falling behind, Williams resorted to her dominating power. She quickly won one game with two aces and two service winners during a stretch when she swept 11 consecutive points.
''In key moments she served really well today,'' Sharapova said. ''Big serves. I got a few of them, but not good enough to get myself back in the point.''
Williams' rhythm and pace improved as the match progressed. She peaked at 122 mph.
''I hadn't been serving great too much this tournament, and then I started serving a lot better today,'' she said. ''I was hitting 120. I was like, 'Whoa. Is that me?'''
Sharapova committed groundstroke errors on the final three points, and a victorious Williams trotted to the net, her left fist leading the way.