* Wawrinka survives rollercoaster start
* Djokovic through to fourth round with walkover (Adds late matches)
By Steve Keating
MIAMI, March 22 (Reuters) - World number one Rafa Nadal launched his bid for one of the few titles to elude him by crushing Australian Lleyton Hewitt 6-1 6-3 on Saturday to reach the third round of the Sony Open.
The Spaniard has won 62 titles, including 13 grand slams and 25 Masters series events, but a victory on the Miami hardcourts is not among them.
Three times Nadal has made it to the Miami final and the Spaniard served noticed that he plans to be back there again after disposing of Hewitt in just over an hour.
World number two Novak Djokovic, a three-time winner in Miami, did not play on Saturday but became the first player through to the fourth round when his scheduled opponent Florian Mayer pulled out with a groin injury.
Australian Open champion Stan Wawrinka survived a rollercoaster start to his Sony Open campaign, advancing with a bumpy 6-0 3-6 6-3 win over Spain's Daniel Gimeno-Traver.
Nadal was happy with his performance against Hewitt.
"I think I played a solid match without many mistakes," he told reporters. "I tried all the time to play the logical shot.
"In general I have to be very happy. I think I did what I had to do today."
With his victory in the opening round on Thursday, Hewitt joined Nadal and Roger Federer as the only active players with 600 or more career wins.
But while Nadal is a champion at the peak of his powers, Hewitt's glory days are behind him, and so it proved in a one-sided contest on Saturday.
"It was tough, I was sort of caught between trying to be too aggressive and too passive," explained Hewitt. "Even when I felt like I was able to push him around he found a way to get back into the point.
"He hit the ball really clean right from the start. I hung in there did everything I could but he was too good."
Third seed Wawrinka, playing just his second event since his milestone win in Melbourne, came out all guns blazing, blasting through the opening set in just 18 minutes.
However, things got much tougher on centre court for the Swiss and he needed nearly an hour and a half to finally tame Spaniard Gimeno-Traver.
"I started well first set," said Wawrinka, now the number one Swiss player ahead of Roger Federer. "It wasn't going that well but I was positive, ready.
"Problem is I still have some up and down mentally.
"I was negative in the second set, a little bit stupid, but then I'm really happy the way I started the third set."
After Wawrinka stormed through the first set and held serve to open the second, the momentum suddenly swung Gimeno-Traver's way and he claimed the early break to go up 3-2 and then broke the Swiss again to level the match.
Wawrinka, however, steadied himself with a break to open third and again to close out the contest.
With the victory Wawrinka pushed his season record to 14-1, a run that includes a pair of titles.
"I know that if I play my best tennis I can be a favourite of the tournament," summed up Wawrinka. "I know how well I can play."
Seventh seeded Czech Tomas Berdych joined Wawrinka in the third round by dispatching Frenchman Stephane Robert 7-6(5) 6-1 while big-hitting Croatian Marin Cilic, the 25th seed, was shown the exit by Frenchman Edouard Roger-Vasselin 6-2 7-6(5).
John Isner continued to carry the American flag, battling back for a 6-7(5) 6-3 6-4 win over compatriot Donald Young.
Isner was left the last American man standing after Canada's big-hitting Milos Raonic, seeded 12th, dispatched Jack Sock 6-4 7-6(1) and Sam Querry was dismissed 6-4 6-4 by Spaniard Nicolas Almagro.
German 13th seed Tommy Haas was a late withdrawal with a sore shoulder, handing Taiwan's Lu Yen-Hsun a walkover into the third round. (Editing by Gene Cherry/Peter Rutherford)