French Open champion Maria Sharapova needed more than three hours to beat Heather Watson of Britain on Tuesday for a place in the third round at the Pan Pacific Open tennis tournament.
The Russian lost a service break while up twice in each set before finally taking the tie 6-7 (7/9), 6-3, 6-4.
Sharapova, 25, struggled with her serve, hitting three double faults in the 10th game of the first set, having to save two set points against her.
She again hit three double faults, one while at advantage on set point at 6-5, and then missed two more points to take the set before losing it, hitting a service return into the net.
But the world number two rallied, attacking Watson's second serve to hit a total of nine service return winners and finish off the match.
"I was not consistent enough. I had opportunities to win the first set and I didn't said Sharapova. "It wasn't the best quality match."
The Russian hit nine aces but also had 14 double faults.
"That certainly gave her a lot of confidence. I think that's the reason why the match was so long. My percentage (of first serves) was very low as well," said the second seed.
"So I put pressure on myself, I hit so many second serves. Certainly I have to improve for tomorrow," she added.
World number one Victoria Azarenka of Belarus maintained her good form to beat Tamira Paszek of Austria 6-1, 6-1.
Fourth seed Petra Kvitova of the Czech Republic became the biggest casualty of the day when the 2011 Wimbledon champion crashed to a 6-4, 6-4 defeat to Petra Martic of Croatia.
A badly off-form Kvitova double-faulted three times to lose the opening game, again lost the first game of the second set to love and was never able to overcome an uphill battle throughout the 88-minute upset.
"She has a big serve and it is tough to push her. She kept me on the defensive and running a lot, and that's not my game. She played so well today, very aggressive," said Kvitova, 22.
Last year's French Open champion Li Na of China, seeded seventh, beat Anastasia Pavlyuchenkova of Russia 7-5, 4-6, 6-2, while ninth seed Marion Bartoli of France defeated Germany's Julia Goerges 6-2, 7-5.