Maria Sharapova and Serena Williams to face off in Sony Open semifinals

Serena Williams continues to look strong as she enters her match with Maria Sharapova. (Mike Ehrmann/Getty Images)

Maria Sharapova and Serena Williams are set to face off in the semifinals of the Sony Open on Thursday, their 18th career meeting. The high-profile matchup has gotten more competitive over the last two years, but once again Sharapova goes in as the underdog of all underdogs. She has not beaten Williams since 2004, losing 14 straight matches and winning just one of the last 22 sets. That one set came here at last year's Miami final, which Williams came back to win 4-6, 6-3, 6-0.

"It's no secret that she's been a big challenge of mine, an opponent that obviously I would love to beat," Sharapova said after defeating Petra Kvitova 7-5, 6-1 in the quarterfinals.

Williams' presence has been a huge roadblock for Sharapova throughout her career. Though her signature win came against Williams in the 2004 Wimbledon final, she has lost to her in six finals, including the 2007 Australian Open, 2012 Olympics, 2012 WTA Championships and 2013 French Open. That's four significant titles Sharapova probably would have won if not for Williams.

"There are certainly ways that I need to step up in certain situations that I haven't been able to do in the past against her," said Sharapova, who is 2-15 against Williams. "But it's great that I have come to that stage and have the opportunity to play her again."

Williams is a six-time champion in Miami. Sharapova is still chasing her first title at Crandon Park; she has reached five finals, including three in a row. Still struggling to find her best form after a shoulder injury ended her 2013 season in August, Sharapova has yet to make a final this season and could fall as low as No. 10 in the rankings if she can't beat Williams.

"When you're playing champions, you have to play your best," Williams said. "She plays her best and her heart out against me -- we just have to bring the best because we're both really good players."

Said Sharapova: "I feel in the last few times I have played I have had my chances and opportunity and something that maybe I didn't quite create, say, a couple years ago. It's about taking those. An opponent that plays with so much confidence and so much power, you really need to take those few opportunities that you have."

Highlights from their last meeting, in the semifinals of the Brisbane International in January. Williams won 6-2, 7-6 (7).

Williams is playing her first tournament since the Dubai Championships in February. Though her form was scratchy through two matches, she had her best performance of the tournament on Tuesday with a 6-2, 6-2 win over Angelique Kerber. Regardless of her form, she never fails to get up for her matchups with Sharapova.

"Well, I love playing her, I really do -- doesn't matter what surface or anything," Williams said. "She's one of my favorite people to play. And so I think that helps when you're playing against people. It just gets you really pumped."

The other semifinal will be decided on Wednesday. No. 11 Dominika Cibulkova will meet No. 3 Agnieszka Radwanska, in a rematch of an Australian Open semifinal that Cibulkova won handily. No. 2 Li Na and No. 18 Caroline Wozniacki will play in the night session.

 This post has been corrected to reflect the fact that Sharapova's last win over Williams came in 2004, and her last tournament was the Dubai Championships, not the Qatar Open.