Rafael Nadal advances on walkover at Indian Wells

A 4.7 earthquake that shook the California desert proved the most exciting moment of Rafael Nadal's Monday morning as he advanced to the fourth round at Indian Wells on a walkover.

The former world No. 1, playing his fourth tournament since returning last month from a seven-month injury absence, was preparing to take to the court when he learned third-round opponent Leonardo Mayer of Argentina had pulled out with a bad back.

"That's bad news, especially for the fans and for Mayer," said Nadal, who was applying tape to his fingers in preparation for the match when he heard.

"I talked with him. It seemed like it's nothing very, very bad -- just a typical back problem beginning when he was warming up his serve."

Mayer's sudden withdrawal left Nadal feeling a little flat, but the Spaniard was quite animated when describing the earthquake, which originated from an epicentre just 30 miles (50 km) from Indian Wells.

"I was very scared. First time in my life," said Nadal, adding he was so alarmed to feel a massage table move beneath him his legs were shaking when he got up.

Nadal, who is playing his first hard-court tournament since a sore left knee forced him out of the semi-finals at Miami last March, said he wouldn't put in a lot of extra practice, but would work out in the gym.

The pass into the round of 16 at the year's first Masters tournament gives Nadal a chance to rest the troublesome left knee, but it also denies him the match experience he says he needs to build on the comeback he began with three clay-court tournaments in Latin America.

He reached the final in his first tournament back, at Vina del Mar, Chile, then won titles in Sao Paulo and Acapulco.

Nadal has said he's not sure how his knee will hold up on the more punishing hard courts at Indian Wells and at the Miami Masters that follows, but he hopes he'll soon be back playing a normal schedule.

In the fourth round he'll face Latvian qualifier Ernests Gulbis, a 5-7, 6-3, 6-4 winner over 20th-seeded Italian Andreas Seppi.

Gulbis is on a hot streak. He won his third career ATP title at Delray Beach last week as a qualifier. Prior to his win over Seppi Gulbis beat Spain's Feliciano Lopez 6-3, 6-2 and in the second round he dispatched ninth-seeded Serb Janko Tipsarevic 6-2, 6-0.