NEW HAVEN, Conn. (AP) -- Martina Hingis outlasted hard-hitting Alexandra Stevenson 7-5, 6-4 Wednesday to advance to the quarterfinals of the Pilot Pen.

The fifth-seeded Hingis, playing in her second tournament since ankle surgery in May, will face unseeded Anastasia Myskina in the quarterfinals. Myskina advanced with a 7-6 (2), 6-2 second-round upset over fourth-seeded Justine Henin.

Hingis got as far as the quarterfinals in her first event back in Montreal last week. The former No. 1 player said she's gaining confidence with each match.

``I feel more comfortable out there now,'' Hingis said. ``I'm not afraid. I know what I can play. Right now, I'll just take any match, any challenge. I probably didn't play my best, but I won.''

The taller, stronger Stevenson backed Hingis off the net for much of the match with 100 mph-plus serves and powerful ground strokes. She had seven aces, while Hingis recorded one.

Hingis waited out Stevenson, however, pouncing on the few off-speed returns and scoring with well-placed drops and passing shots. She converted five of six break points.

``When I needed to step it up I was able to do so,'' Hingis said.

Despite controlling the match tempo, Stevenson came undone with 45 unforced errors compared to Hingis' 15.

``I just got sloppy,'' said Stevenson, still looking for her first singles title. ``I can play with these girls and there's no reason she should walk off the court the winner. But she did because of my errors.''

Stevenson is 0-4 against Hingis, failing to win a set. She came close Wednesday while serving at 5-4 in the first set. She blew a 109 mph first serve past Hingis and was stunned when it was called out.

``That was on the line and it was a pretty bad call,'' Stevenson said. ``The next time I need to brush it off and say `It happens in tennis' and move on. It's the whole match, not just a set.''

Hingis returned the second serve and Stevenson volleyed back into the net. She made two more unforced errors to lose the set and dropped the next five games.

Stevenson's booming serve, which kept her the match, eventually took her out as she double-faulted for match point.

``I just need to get my serves tougher at the right time,'' Stevenson said. ``It was in my hands to make or break it, and I broke it.''