Rafael Nadal was denied the Chile Open title on his comeback from injury as Argentina's Horacio Zeballos came from a set down to beat him in the final, according to BBC Sport.
Zeballos, ranked 73rd in the world, won his first ATP Tour title with a shock 6-7 (2-7) 7-6 (8-6) 6-4 victory at the clay-court event in Vina del Mar.
Former world number one Nadal, 26, was playing his first tournament after eight months out with knee trouble.
"It's true I wanted to win the final but it wasn't possible," he said.
Zeballos did not progress beyond the second round in any of the tour-level events he competed in last year, but had already beaten three seeds en route to his match against Nadal.
"It's a dream for me," the 27-year-old told the ATP Tour's official website. "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."
Before this week, Nadal had not played a competitive match since suffering a shock second-round defeat by Lukas Rosol at Wimbledon last year.
Having suffered with a knee injury, the world number five pulled out of January's Australian Open with a stomach virus.
Nadal, though, was positive in defeat, despite missing out on his 37th clay-court title.
"It was a great tournament for me," he said. "I just need to keep working, practising with hope, motivation and the right attitude to have better sensations every week. I hope it's the beginning of a lot of good things for me."
