MIAMI (REUTERS) - Tennis' world No.1 Serena Williams overcame a wobbly start to open the defence of her Sony Open crown with a spirited 7-6 (9-7), 6-2 win over Kazakhstan's Yaroslava Shvedova on Thursday.

Fourth-seeded Russian Maria Sharapova, who lost to Williams in last year's final, turned in a steady opening effort after a shock third-round exit at Indian Wells last week, brushing past Japan's Kurumi Nara 6-3, 6-4.

A six-time winner on the Miami hard courts, Williams' second-round meeting with the 59th-ranked Shvedova was expected to be little more than a tune-up for the 17-time Grand Slam winner but for a brief moment the match delivered some unexpected suspense.

"She was doing a little bit of everything," Williams told reporters. "She was hitting hard; she was hitting soft; she was doing a little bit of everything.

"I was making a little more errors than what I should have been making, what I should've made, and that kind of threw me for a loop, as well.

"She was up a break (in the first set) and I started just really trying to fight to make the shots.

"And then when she was serving for the first set I really just tried to be more Serena like."

The contest began with Williams seizing control 3-1 but Shvedova had a sparse centre-court crowd buzzing after breaking the American twice on the way to a 5-3 lead.

But with Shvedova serving for the match, Williams showed why she is the sport's dominant player breaking her opponent and forcing the opening set to a tie-break.

In the tie-break, Shvedova, who had never taken a set off Williams in three previous meetings, surged ahead 6-3 but then crumbled under the mounting pressure, double-faulting before the defending champion blasted a pair of aces past her.

Williams then clinched the set in emphatic fashion, a crushing forehand followed by an equally forceful fist-pump.

After trading breaks to open the second set, Shvedova would hold serve before a focused Williams moved in for the kill, sweeping the next five games to secure passage to the next round.

"It's definitely going to help, knowing that I was able to pull that through after being down pretty drastically," said Williams, will next face Frenchwoman Caroline Garcia, who advanced to the third round with a 7-6 (7-3), 7-6 (7-3) upset of 27th seed Klara Zakopalova of the Czech Republic.

A five-time runner-up in Miami, Sharapova has her sights firmly set on finally making the Miami's winner's circle but will not face a re-match in the final against Williams, with both on the same side of the draw.

"Obviously I have been close, and I have had my fair share of chances of winning the tournament," said the Russian four-time Grand Slam champion. "Obviously I'm still looking for that.

"But with that said, I have had really great experiences, great matches with her, and it would be really special if I could win it, for sure.

"I expect to win because I have won before. I have won tournaments before."

It was smooth passage for all the top 10 seeds in action.

Fifth-seeded German Angelique Kerber, twice a finalist this season, narrowly avoided an early exit and needed a tie-break to tame China's Peng Shuai 6-3, 1-6, 7-6 (7-5).

Eighth-seeded Czech Petra Kvitova advanced with a straight-forward 6-3, 6-4 win over Argentinian Paula Ormaechea. Italy's Sara Errani, the ninth seed, eased past Austrian Patricia Mayr-Achleitner 6-1, 6-4.

Serbia's Ana Ivanovic, seeded 12th, raced into the third round with a 6-1, 6-1 demolition of American Lauren Davis, while Italy's Flavia Pennetta, riding the momentum from her BNP Paribas Open win at Indian Wells on Sunday, moved on with a 6-3, 6-3 win over Belarusian Olga Govortsova.

Former US Open champion Sam Stosur of Australia, the 16th seed, was an easy 6-3-6-2 winner over Netherlands' Kiki Bertens.