Maria Sharapova reached the US Open's fourth round by taking five of the last six games after her opponent, Sabine Lisicki, was warned by the chair umpire about receiving coaching help.
Avoiding the sort of surprise that saw half of the top eight seeded women lose already, No. 5 Sharapova eliminated No. 26 Lisicki 6-2, 6-4 in a hard-hitting match that began Friday night (Saturday NZ time) and ended past midnight Saturday.
''She's a very dangerous and tricky opponent, and she's capable of playing really well at the Slams and always raising her level against the top players,'' Sharapova said.
''That was something I was very well aware of. I thought I stepped up to the challenge.''
Five-time major champion Sharapova trailed 3-1 in the second set. But she turned things around as 2013 Wimbledon runner-up Lisicki went back and forth with chair umpire Carlos Ramos over whether she was getting instructions from her entourage.
"I didn't know what he meant,'' Lisicki said. ''I didn't see anything. I wanted to know what it was that he saw, because I haven't seen it.''
Still, Sharapova did not wrap things up easily against Lisicki, who at a hard-court tournament in Stanford, California, last month hit the fastest recorded serve in the history of the WTA, reaching 131 mph (211 kph).
Sharapova got broken while serving for the victory at 5-3, then needed three match points to close it with her sixth break of Lisicki.
''A very aggressive, big server,'' said Sharapova, who will play 2009 US Open finalist Caroline Wozniacki for a spot in the quarterfinals.
''I just tried to concentrate on my return. I wasn't serving as well as I wanted to.''
The point of the match came with Lisicki serving and already ahead 2-1 in the second set. She raced this way and that along the baseline, scrambling for a forehand retrieval, then to the other side for a backhand to extend the point, before returning to her forehand side for a desperation defensive lob.
Eschewing an overhead, Sharapova let the ball drop but badly missed a forehand that landed way out. That saved a break point and Lisicki held to go ahead 3-1.
But that's when Ramos was beginning to engage Lisicki in a discussion about whether her coach was sending her signals.
In WTA tournaments, coaches are allowed to head down to the court between games and help players during matches. But coaches are not allowed to give tips to their players in Grand Slam matches.
''Let's talk at the changeover,'' Ramos told Lisicki, and when she sat on the sideline at 3-2 in the second set, the conversation resumed.
''I know what I saw,'' Ramos told her. He suggested to Lisicki that she tell the folks in her guest box not to offer suggestions.
Before serving in the next game, Lisicki wandered toward the stands, carrying balls on her racquet, and said something toward her guest box, then shrugged her shoulders.
Moments later, on break point, Lisicki sailed a swinging forehand volley well out, allowing Sharapova to pull even at 3-all.
Asked at her news conference what she told her group before that game, Lisicki said: ''That he thought they were coaching, just so they were aware.''