Serena Williams set up a quarter-final against Amelie Mauresmo after beating Nadia Petrova at the Australian Open.
The American, seeded seven, was seemingly cruising into the last eight after comfortably taking the first set.
But a rejuvinated Petrova clubbed her way back into the game, a turnaround that left Williams claiming the Russian was receiving court-side coaching.
Hostilities between the pair increased in the tense decider which Williams re-grouped to win 6-1 3-6 6-3.
"I didn't deserve to win the way I played," Williams said after her victory.
"My serve was horrible. I've worked really hard on it. It's just, I'm a perfectionist, and I played really bad.
"I don't see too many positives out of except I think I ran well for it on some dropshots. That's about it."
Second seed Amelie Mauresmo enjoyed an easy passage into the last eight of the Australian Open with a 6-2 6-4 win over unseeded Russian Evgenia Linetskaya.
Mauresmo started strongly and sped into a 4-0 lead, but after losing her serve required lengthy off-court treatment.
The Frenchwoman returned with heavy strapping on a thigh injury but it failed to slow her progress in a match dominated by long baseline rallies and breaks of serve, of which there were 11 in total.
Mauresmo insists the injury will not force her to pull out of the tournament.
"It's nothing bad," she explained. "The adductor got a little bit tight. I just didn't want to take any risk.
"I preferred to put the prevention tape on to make sure nothing bad happens.
"I feel good. I feel my game is really solid. I know I have to improve a little on the serve but that's probably the only point that I have to work on."
Maria Sharapova recovered from a slow start to beat Italy's Silvia Farina Elia 4-6 6-1 6-2.
After losing the first set, Sharapova looked in real trouble when she dropped her opening service game in the second.
But it precipitated a sparkling return to form during which she broke back three times to set up a deciding set.
However, the fourth seed soon lost her way again in a scrappy finale before securing an unconvincing victory.
Despite the nature of the win, Sharapova is not bothered by her fluctuating form.
"She played a solid game. She hit great winners out of the court which sometimes were unexpected, but I hung in there and fought well," she said.
"I was just letting her play her game and worrying about what she was doing.
"I'm just excited to be in the quarters. I'm just going to go out there like I have been, playing my game, having fun, enjoying it and fighting to win."
Sharapova now faces compatriot Svetlana Kuznetsova who was then first woman to reach the quarter-finals.
I think she's all right - she's a bit different, like each of us, we are all different
But the Russian, who has been dogged by doping allegations during her time in Melbourne, was far from convincing in beating compatriot Vera Douchevina.
The powerful US Open champion and number five seed took time to settle and made a string of unforced errors.
However, she finally found some rhythm late in the match and won five games in a row to close out for a 6-4 6-2 win.
"I think there is a little bit to get in my game and I hope next match I'm going to play better. Well, I have to," the 19-year-old said.
"Definitely when I play Grand Slams it's not enough for me to pass two or three rounds - I want to go higher and higher."