MADRID, Spain - In a highly-anticipated clash between two Grand Slam champions, No.8 seed Sloane Stephens outlasted Victoria Azarenka in a second-round meeting at the Mutua Madrid Open, 6-4, 2-6, 6-2.

The former US Open champion edged a tight first set - breaking Azarenka from 40-0 to seal the first set - but ultimately needed to win the last four games of the match to reach the third round.

The win is Stephens' fourth straight against Azarenka, having lost the first three of their seven career meetings.

"Playing Vika is always really competitive. She's a good player, a great champion. I just tried to play my game, focus on what I was supposed to be doing," Stephens told WTA Insider after the match.

"In the second set, she raised her game a little bit and I dropped overall. Overall, I thought it was a super-competitive match, and we both played well."

Stephens served well throughout the contest, never facing break point against Azarenka's famed return in the opening set, and dropped serve for the first time in the third game of the second.

Raising her level impressively and showing the form that took her to the championship match in Madrid in back-to-back seasons in 2011 and 2012, Azarenka won six of the seven games played after Stephens held serve to begin the set to force a decider.

"I felt that I really was taking all the control from the baseline points. I felt that I was doing the right things. I was moving the ball around. I was moving well, and I was playing smart tennis," Azarenka said in defeat.

"I didn't create anything with my serve today and it was really frustrating. I didn't really have a game plan. There was really no game plan of what to do with the serve and that is something I need to take a look at and fix.

"The good point is that with all that, I was still able to create those opportunities to take that. It's going to be a good lesson learned for me and I'll move on.

I slipped up the game at 5-4, which I had full control of. So those are the little things that I have to do a little better and just trying to make the serve in isn't going to help.

"I'm frustrated obviously that I didn't do the best things on that today, but I'm happy with a lot of other things that I've done well and I just need to continue to work for them, the bigger goal. So I'm going to continue to do that."

Overall, Stephens won 73 percent of her first serve points in the match, getting back on track behind her delivery in the decider.

She saved both break points she faced - in a key 1-1 game that kept her in front - and took advantage of four of Azarenka's nine double faults to break serve twice, and seal a spot in the third round in two hours and five minutes. 

"I think it's better to play competitive matches like that early on, so you can get the juices flowing and get everything the way it should be," Stephens said. 

"Overall, that match today is really helpful for the next few weeks in a row."

The American will next face the winner of the second round match between Zheng Saisai and Alizé Cornet.