Serena Williams reaches Indian Wells last 16

Serena Williams hit five aces in her straight sets win over Zarina Diyas

World number one Serena Williams is through to the last 16 at Indian Wells after completing a 6-2 6-0 win over Zarina Diyas of Kazakhstan.

She now meets fellow American Sloane Stephens after a 53-minute victory in the BNP Paribas Open third round.

Williams, who boycotted the event for 14 years after being booed and heckled in 2001, says she now feels comfortable playing at the California tournament.

"It definitely felt back to normal out there," the 33-year-old said.

"I was able to relax because I was able to do more of the right things and not make as many mistakes as I did in my last round."

Stephens beat two-time major champion Svetlana Kuznetsova 7-6 (7-4) 1-6 6-4 to set up the last-16 meeting with Williams.

Switzerland's Roger Federer beat Diego Schwartzman 6-4 6-2 in the second round of the men's tournament.

The four-time Indian Wells winner, who is now two short of 50 wins at the event, says his mobility around the court was the biggest factor in his 63-minute victory over the Argentine.

"I'm moving well, which is key on this surface because the easy shots and easy points are not going to happen so easily here like they maybe do in Dubai or Australia or the indoor season," Federer, 33, said.

The world number two will face Andreas Seppi, who beat him in the Australian Open third round in January.

Seppi advanced with a 6-4 6-4 win over Romania's Victor Hanescu.

"I'm happy I'm getting an opportunity to play him right away again," Federer said.

Three-time champion Rafael Nadal dropped just seven service points as he beat Igor Sijsling 6-4 6-2 to set up a fourth-round meeting with Donald Young of the United States. Nadal's fellow left-hander Young beat France's Jeremy Chardy 6-4 6-2.

"I moved a little bit quicker than what I was doing one month ago," Nadal said.

"I was able to defend some points well, to have some good passing shots, have some winners, some good shots down the line with my forehand. That always gives me a lot of confidence."

Earlier, British number one Heather Watson pulled off the biggest win of her career, beating world number eight Agnieszka Radwanska 6-4 6-4.

Serena Williams converted six of her 12 break opportunities against 28th-seed Zarina Diyas

Williams was close to tears in her first match for 14 years at Indian Wells on Friday

Roger Federer has won two ATP World Tour titles this season. in Dubai and Brisbane

Rafael Nadal won 96% of his first-service points against Igor Sijsling