Horacio Zeballos denied Rafael Nadal a fairytale finish to his comeback tournament, rallying to hand the Spaniard a rare clay court defeat in the $410,200 ATP event here.
Zeballos, ranked 73rd in the world and playing in just his second ATP Tour final, rallied to beat the former world number one 6-7 (2/7), 7-6 (8/6), 6-4.
He became just the third player -- along with Novak Djokovic and Roger Federer -- to beat Nadal in a clay court final, quite an achievement for the Argentinian despite the fact that Nadal was playing his first tournament in seven months.
"It's a dream for me," said Zeballos. "To be able to play a final against Nadal was already good enough for me. It's a moment that will stay in my memory for the rest of my life."
Nadal was back in action this week for the first time since a surprise second-round exit at Wimbledon in June.
Since then he had been sidelined by a torn tendon and inflammation in his left knee, with his return this year further delayed by a virus.
Now ranked fifth in the world, 11-time Grand Slam champion Nadal was the top seed and had lost just 14 games en route to the final.
"It was a great tournament for me," Nadal said. "If we take everything, it was positive.
"It's true I wanted to win the final but it wasn't possible. He made things better than me and I didn't play my best match.
"I just need to keep working, practising with hope, motivation and the right attitude. I hope it's the beginning of a lot of good things for me."
Neither player managed a break of serve in the first two sets. They traded breaks in the first two games of the third before Zeballos -- clearly gaining confidence -- broke Nadal at love in the final game to wrap up the victory in two hours and 46 minutes.
Nadal had saved two break points in his first service game of the first set -- the only break chances of the opening frame.
He dominated the tiebreaker but once again in the second set Nadal couldn't break through against Zeballos' potent serve.
Zeballos saved two break points in the fourth game, and worked out of a 15-30 jam in the 10th to hold serve and knot the set at 5-5.
Looking poised in the second-set tiebreaker, Zeballos gave himself two set points with a service winner for 6-4. Nadal saved both, but Zeballos gained another chance with a sizzling service return for 7-6 and duly pocketed the set.
"I've worked really hard because I really wanted to be at this level," Zeballos said. "For some months, I've been playing at a high level and I think I'm at the best moment of my career. I'm very strong physically and psychologically."
Nadal returned to the court later, teaming with Argentina's Juan Monaco where they lost in the doubles final to Italians Paolo Lorenzi and Potito Starace 6-2, 6-4.
The 26-year-old had played down his expectations coming into the week, saying he still felt some pain in the knee and just wanted to get in as many matches as possible to regain his sharpness.
He plans to compete in clay court events in Brazil and Mexico before playing ATP Masters hard court events at Indian Wells and Miami and then heading to Europe for clay events in Monte Carlo, Barcelona and Rome ahead of the French Open.
Nadal's triumph at Roland Garros last year was his 11th Grand Slam victory -- and his most recent title.
Zeballos, who posted his first win over a top 10 player in three attempts, joined Aussie Bernard Tomic as first-time winners on the tour this year.