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Puerta, who won the Casablanca Open last week, came through 7-6 1-6 6-3.

Australian Open champion Marat Safin earlier eased past South Korea's Lee Hyung-Taik 6-0 7-5, and Olivier Rochus beat eighth seed Ivan Ljubicic 6-2 6-2.

Gustavo Kuerten's hopes of a third Monte Carlo crown were dashed 7-5 6-2 by 13th seed Mario Ancic.

Moya has now lost three times to Puerta this year, and said: "I was unlucky to be drawn against him in the first round.

"There are lots of players who I could have drawn who are not clay-court specialists, or were playing their first match of the season on clay.

It's hard to play your best tennis when you have been out for such a long time Gustavo Kuerten

"This was a chance to win a few matches. He is clearly giving me trouble at the moment, he's very confident right now."

Second seed Safin, who suffered early exits at the Indian Wells and Miami Masters, won the first set of his match in just 20 minutes before deciding to experiment.

The 25-year-old Russian revealed: "I wanted to try some different things.

"It's better to do it in the first round rather than against a clay-court specialist in the semi-finals."

Safin will now play France's Cyril Saulnier.

Kuerten only returned to action last week in Valencia after being sidelined for six months because of more hip surgery.

"I am 65% of my best at the moment but I think I will be up at 80% by the time of the French Open," he said.

"It's hard to play your best tennis when you have been out for such a long time, but I felt no pain today and that's a win for me. It's more important than the match.

"If I can continue like this, I will be the happiest man in the world by the end of the year."

In other matches, Jean-Rene Lisnard beat 12th seed Thomas Johansson 4-6 6-4 6-2, and David Ferrer saw off 14th seed Dominik Hrbaty 6-4 6-3.