Mariano Puerta reached his first Grand Slam semi-final at the French Open on Wednesday, the Argentine's return to top flight tennis complete following a nine-month anti-doping ban.

The 26-year-old, who has hauled his ranking up from 440 to 37 after testing positive for the banned drug clenbuterol in 2003, outgunned compatriot Guillermo Canas 6-2, 3-6, 1-6, 6-3, 6-4.

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"I can't believe I've reached the semi-finals, I really want to enjoy this moment," he said.

Clenbuterol promotes muscle growth. An anti-doping tribunal determined last year that Puerta had been prescribed the drug by a doctor to treat an acute asthma attack.

The player has always denied any wrongdoing and said on Wednesday his exile had made him stronger.

"I don't really feel bitter," he added. "I just don't think back ... don't waste my energy remembering things in the past. But I think it helped me to be stronger psychologically today, since every victory for me is even more important.

"When you go through a rough period, I'm sure that it just makes you become stronger. It's hard for people to sink you.

DIFFICULT MOMENTS

"Everything I went through helps me feel calmer, and it has helped me mature and overcome difficult moments."

Puerta will face Russian Nikolay Davydenko in Friday's semi-final. The 12th seed beat Spaniard Tommy Robredo 3-6, 6-1, 6-2, 4-6, 6-4.

In the top half of the draw, world number one Roger Federer [Images] will face fourth seed Rafael Nadal [Images].

Both Puerta and Canas learned their trade on the slow clay courts of Buenos Aires, and a long, tough test of patience and stamina was expected. Neither player disappointed.

Ninth seed Canas had been the favourite but on the Roland Garros centre court there was nothing to separate the former junior team mates.

For five sets the energetic Canas scurried and chased, shovelling the ball back with his compact, economic strokes.

Puerta, a runner-up in the boy's singles here in 1995, threw everything at his opponent, his looping left-handed shots finding ever-more acute angles before Canas cracked for the last time.

The 27-year-old ninth seed simply ran out of ideas.

"I think if I could go back and change something, I'd change Puerta," he laughed.

TOUGH BATTLE

"I was disappointed. I think disappointed is the right word. My expectation was to be in the semi-finals, and it was a very tough battle between the two of us.

"I think I did everything I could do to be in semi-finals.

"When the match ended, well, I think I felt disappointment, some small disappointment.

"But, you know, it's a tennis match and somebody has to lose."

Davydenko outlasted Robredo in a tight five-set tussle.

"The key was to run, to run for every ball," the Russian said. "It was so tough. Robredo played so well. He is a better player from the baseline but I managed it."

The Russian, who turns 24 on Thursday, made sure of entering the world's top 10 when the new rankings are released on Monday.

"First time in the semi-finals of a Grand Slam, first time in the top 10 -- this is my birthday present," he smiled.

"Right now I'm tired but tomorrow I'll realise and it will feel good."

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