Former winners Roger Federer and Rafael Nadal breezed through with straight-set wins on Sunday as a flu bug wreaked havoc on the men's and women's draws at the Indian Wells tournament. Reigning Wimbledon champion and WTA Player of the Year Petra Kvitova was knocked out early when 19-year-old American Christina McHale fought back to beat the Czech in three sets. But the biggest problem eating into the draw Sunday was a stomach virus that has forced at least eight players to withdraw or retire within the last two days, including men's 14th seed Gael Monfils and women's ninth seed Vera Zvonareva.

Third seed Federer defeated wild card Denis Kudla 6-4, 6-1 in a second round night match on centre court. The Swiss master said he was also feeling a bit sick, but not as bad as his family members and not enough to be thrown off his game. Federer hammered eight aces and won 79% of his first serve points in the 57 minute contest. "We are fighting something of our own in our family," said Federer who is travelling with his wife and two young twin daughters.

"I have a bit of a combination. Not a terrible temperature but I have some things going on. I am the best off in the family. The rest of them are struggling much more." Federer, who won Indian Wells three straight years from 2004-2006, advances to the third round where he will face hard-serving Canadian Milos Raonic, who beat Carlos Berlocq in straight sets 6-4, 6-2. It will be the first career meeting between the former world number one Federer and Raonic who has already won two singles titles on the tour this year.

"I am looking forward to that match," Federer said. "He's a good player and up and coming. Sometimes it can help and sometimes it cannot help to have never played a guy before." Nadal, a two-time Indian Wells champ, routed Leonardo Mayer 6-1, 6-3. It marked the Spaniard's first match since losing to world number one Novak Djokovic in a monumental five hour, 53 minute final at the Australian Open. "It's fantastic. I am happy to start with a victory," the world number two said.

"I am taking it day by day. It's not easy to be back after a while without competition. "I started the match very focused, very aggressive. Today the only thing I can say is I'm very happy." Nadal advanced to the third round, where he will face fellow Spaniard Marcel Granollers, who beat Tommy Haas of Germany 6-3, 2-6, 6-3. The left-handed Nadal hit one ace, posted two double faults and won four of six break point chances.

Ninth seed Juan Martin del Potro defeated Australia's Marinko Matosevic 7-5, 6-2 in their second round match. Sixth seed Jo-Wilfried Tsonga advanced to the third round when Michael Llodra pulled out of their all-French clash with a knee injury. Tsonga was ahead 4-1 in the first set when Llodra packed it in. On the women's side, McHale rallied to upset Czech Kvitova in three sets 2-6, 6-2, 6-3.

"She's moving very well, so she played a lot of shots back," Kvitova said. "My serve was not too good. So it was tough." McHale finished the match by winning her service game to nothing, with a backhand slice winner sealing the victory. "I just kind of hung in there early in the second. She played one service game where she gave me a couple of loose errors and then I just kind of kept hanging in there, and then I got more comfortable as the match went on," McHale said.

Top seed Victoria Azarenka defeated two-time grand slam winner Svetlana Kuznetsova 6-1, 6-2, extending her season-long winning streak to 19-0. World number one Azarenka advanced to the fourth round where she will face Julia Goerges who beat Anabel Medina Garrigues of Spain 6-3, 6-4. Azarenka faced Goerges three times in 2011, winning two semi-finals encounters at Madrid and Luxembourg.