The fifth-ranked Sharapova, who reached the Wimbledon final, questioned an out call that would have ended the match. She regrouped and won the next two points to set up the possible match between two former world No. 1s.
"It's still about improving the little things to get more consistent," Sharapova said. "I've had to make a lot of tough choices in the last year but I'm going in the right direction and, little by little, those choices are paying off." Williams, playing in her first tournament on American soil since the 2009 U.S. Open, meets Maria Kirilenko on Thursday afternoon.
"I've lost to both of them the last time I played them," Sharapova said. "You can never rest against Serena. She hasn't played in quite a while but she's still a great competitor. At the end of the day she has 13 Grand Slam titles and I have three. That says a lot. Maria can produce great tennis and beat top players." Sharapova got off to a slow start against Hantuchova before finishing strong in the first set.
"Then I kind of lost it," Sharapova said. "I got away from what I was doing well and she had all the confidence and all the momentum going into the third set." Hantuchova grabbed a 2-0 lead in the third set before Sharapova regained the momentum and won four straight games to finish it off.
"I was frustrated by the fact I wasn't able to maintain what I was doing into the second set," Sharapova said. "I was able to break her back and got the energy going again." Hantuchova knew that was the turning point.
"Leading 2-0 in the third set, that next game was crucial," Hantuchova said. "She went on that unbelievable run and that's where it changed a little bit. Even though I wasn't playing my best tennis, I still felt like I had so many chances. I think I had 12 break points on two of those. It was a good fight." France's Marion Bartoli reached her seventh quarterfinal of the year, beating Rebecca Marino of Canada 6-4, 6-3.
The ninth-ranked Bartoli, who won this event two years ago, has won 18 of her last 21 matches.
"I love this tournament. It's a great way for me to start back," Bartoli said. "I lost to Rebecca last year in Quebec, so it was good for me to take revenge. I really felt like I was moving well. I was hitting the ball well for having three weeks off." Marino, ranked 40th, beat Bartoli at Quebec City last year _ her only win over a top-20 player.
In other matches, eighth-seeded Dominika Cibulkova of Slovakia beat American Christina McHale 6-4, 2-6, 6-3, and fifth-seeded Agnieszka Radwanska of Poland topped Taiwan's Chang Kai-chen 6-4, 3-6, 6-0.
"It was really difficult to play," Cibulkova said. "I didn't play my best and it's not always easy to win matches like this." The 20th-ranked Cibulkova reached her seventh quarterfinal of the year and will meet the winner of Thursday's match between top-seeded and defending champion Victoria Azarenka and qualifier Marina Erakovic.
"Sometimes a match like this gives you more confidence because you have to fight and play through it when you are struggling. Now in the next match, you can play even better knowing you just won a real tough match."