Nadal, Federer march ahead

World number two Rafael Nadal raced into the third round of the ATP Indian Wells Masters as Roger Federer made a less speedy but still successful start to his quest for a sixth title.

Nadal, a three-time Indian Wells winner, needed just 72 minutes to get past Jared Donaldson 6-1 6-1 on Sunday.

Federer, who is seeking to break out of a tie with top seed Novak Djokovic for most titles in the California desert, looked set for a similarly easy time of it, but had to turn back a second-set challenge from German Peter Gojowczyk in a 6-1, 7-5 win.

Fourth-seeded Federer said he was relieved not to go to a second-set tiebreaker after falling behind 3-1 to the free-swinging German who is ranked 85th in the world.

The Swiss regained the break and, after saving four break points to make it 4-4, he broke Gojowczyk for a 6-5 lead, the German double-faulting on break point to give Federer a chance to serve it out.

Nadal, playing his third tournament of a year that started with a crushing loss to Djokovic in the Australian Open final and included an early exit in Acapulco, converted five of his six break chances against Donaldson and never faced a break point himself.

He next faces Diego Schwartzman, who beat Spain's Roberto Carbralles 6-3, 6-1. Nadal is 6-0 against the Argentinian.

In other early matches, sixth-seeded Kei Nishikori of Japan survived a scare in a 6-4, 4-6, 7-6 (7/4) victory over France's Adrian Mannarino.

Nishikori next faces 67th-ranked Hubert Hurkacz of Poland, who defeated France's Lucas Pouille 6-2 3-6 6-4.

Eighth-seeded American John Isner routed Australian qualifier Alexei Popyrin 6-0 6-2, the most lopsided win of Isner's career.

Tenth-seeded Croatian Marin Cilic downed Serbian Dusan Lajovic 6-3 6-4 to book a meeting with 19-year-old Canadian Denis Shapovalov, the 24th seed who beat American Steve Johnson 6-3 6-4.

Serena withdraws

The women's event lost 23-times Grand Slam winner Serena Williams, who retired against Garbine Muguruza with what organisers described as a viral illness. The Spaniard was ahead 6-3 1-0 at the time.

Former Wimbledon and French Open champion Muguruza was happy with the way she had been playing against Williams before the American's retirement.

"I think I played well," she said. "I'm going to take the positive side of that."

World number two Simona Halep survived a tough challenge from Ukrainian qualifier Kateryna Kozlova to win their third round match 7-6(3) 7-5.

Sixth seed Elina Svitolina, looking for her first title of the year, beat Daria Gavrilova 7-5, 6-4 to advance while world number seven Kiki Bertens reached the fourth round at Indian Wells for the first time after a 7-6(10), 6-4 win over Briton Johanna Konta.

Bertens will next meet Muguruza.