Andre Agassi lost to Nikolay Davydenko, then pulled out of the Tennis Masters Cup less than an hour after second-ranked Rafael Nadal withdrew with an injured left foot.

Nadal withdrew Monday while Agassi was on court, losing 6-4, 6-2. The 19-year-old Spaniard had been due to face Gaston Gaudio in his opening round robin-match in the Gold Group.

Mariano Puerta became the fourth Argentine player in the draw when he was drafted to play compatriot Gaudio in Monday's later match at Qi Zhong Stadium.

Fernando Gonzalez of Chile will take Agassi's place in two remaining round-robin matches in the depleted Gold Group.

Top-ranked Roger Federer, also on the comeback from injury, leads the Red Group. He overcame Argentine David Nalbandian in his opening match Sunday.

Argentine Guillermo Coria and Ivan Ljubicic are in Federer's group.

Agassi lasted 1 hour, 14 minutes against Davydenko, then said he couldn't play the rest of his round-robin matches because he aggravated an injury in his left ankle.

"No chance for me to play again - it's very dangerous and risky for my future," Agassi said. "This is an unfortunate setback."

Nadal said he had consulted local doctors in Shanghai and the tournament doctor, and all recommended he withdraw and rest the damaged ligaments in his foot.

"I had a lot of inflammation in the foot after Madrid," Nadal said. "After I came here, I had more pain."

The two latest injuries are a major setback for the season-ending Masters Cup, which is supposed to feature the top eight players of the year.

No. 3 Andy Roddick and Australian Open winner Marat Safin withdrew before the tournament because of injuries. Lleyton Hewitt, ranked fourth, opted to remain in Sydney with his wife, actress Rebecca Cartwright, who is expecting the couple's first child within two weeks.

Defending champion Federer was officially recognized as the winner of the 2005 ATP Champions Race before play on Monday. He had an unbeatable lead in the season standings ahead of the Masters Cup.

"I haven't lost my No. 1 ranking this year so I will try to keep it up and who knows, I could be standing here in 365 days' time," Federer said.

He won 11 titles, including Wimbledon and the U.S. Open, and had a 78-3 singles record coming into Shanghai, where he is aiming for a third consecutive Masters Cup title.

(Agencies)