"Sanchez played a great match from the beginning and I couldn't respond," said Kuerten, the fourth seed.

"I knew I wasn't going to play my best tennis in this match because I am feeling sick."

Kuerten arrived in Argentina with flu-like symptoms after losing in straight sets to Fernando Gonzalez in Vina del Mar.

"I hurt all over my body and I feel very tired," added Kuerten. "I wanted to play, however, because I didn't want to disappoint the people coming to watch me.

"I am taking medicines now and most important is to get better."

It was Sanchez's second most impressive win of his career, following his victory over then-world number one Andre Agassi in the first round of last year's Tennis Masters Series event in Rome.

Sanchez now faces defending champion Carlos Moya, the second seed who overcame an injury to advance, hobbling past Harel Levy of Israel 6-2 6-4.

He had not competed since retiring in the final of last month's Adidas International.

"My ankle was better than I thought it was going to be a week ago," the Spaniard said. "If I keep earning confidence, I can be a candidate for the title this year again."

Three seeded Argentinians gave the home crowd something to cheer about by booking their places in the second round.

Fifth seed Agustin Calleri thrashed Galo Blanco of Spain 6-4 6-2, sixth Mariano Zabaleta defeated Frenchman Jean-Rene Lisnard 6-4 6-4 and number eight Juan Ignacio Chela beat Giovanni Lapentti of Ecuador 7-5 6-0.

Of the eight players from Argentina in action, seven moved on, including Jose Acasuso, who defeated seventh-seeded countryman Gaston Gaudio 6-3 7-6 (8/6).

Also moving into the second round were Juan Monaco, Franco Squillari and Diego Moyano.

Olivier Patience of France, Flavio Saretta of Brazil and Spaniard David Sanchez complete the second-round line-up.