Top seed champion Maria Sharapova needed more than three hours to beat Anabel Medina Garrigues and advance to the quarter-finals of the Amelia Island Championships on Thursday.
Sharapova took a marathon three hours, 27 minutes to win her match 7-6, 5-7, 7-6 as both players slugged it out from the baseline.
Sharapova will join fellow Grand Slam winner Amelie Mauresmo in the quarter-finals after the 11th-seeded Frenchwoman overcame a first-set wobble to defeat Agnieszka Radwanska 3-6, 7-5, 7-6.
""There were a lot of ups and downs in the match. I think I should have won the match in two sets to be honest," Sharapova told reporters. "But I stopped hitting the ball and I kind of let her back in the match."
Sharapova, who had held a 5-3 lead in the final set but then been rattled by a controversial line call in the ninth game, was struggling at 5-6 before she dominated her service game to send the final set into a tiebreak.
The tall Russian had no problems in the tiebreak, running out a 7-1 victor.
"When you're down 5-6 after being 5-3 up, you're just trying to think of the right things and just focusing on what you have to do in order to win point by point," Sharapova said.
"I played a really good game to get it even, and I just thought 'You have to do the same thing in the tiebreaker'.
"In those situations, after three hours or so, it all comes down to the heart and how tough you are. The forehands or backhands don't mean much after that."
Sharapova will now meet 10th seed Alona Bondarenko, who also advanced with a three-set victory over sixth seed Dinara Safina 7-6, 0-6, 7-5.
Mauresmo successfully landed 86 percent of her first serves in the opening set but her Polish opponent was able to record the only service break.
The 28-year-old Frenchwoman recovered in the second set and won the third-set tiebreak over the seventh seeded Radwanska 8-6.
In the quarters, Mauresmo will face the winner of the match later on Thursday between second seed Anna Chakvetadze and Dominika Cibulkova of Slovakia.