Rafael Nadal was shocked by Novak Djokovic's loss at the Rio Olympics, but said no more could be expected of the "unbelievable" Serbian.
World number one Djokovic was stunned by Juan Martin del Potro in the first round at the Games, extending his wait for an Olympics gold.
Djokovic has enjoyed another incredible year, winning the Australian Open and his maiden French Open title.
Nadal, returning from a wrist injury, has fared much better in Rio and is into the third round, but he was stunned by Djokovic's loss.
"When the best player of the world loses it's always a surprise," the Spaniard said.
"We cannot demand more of Novak. I think what he's been doing is something unbelievable and he can lose sometimes.
"His success is something difficult to repeat. It's normal that in some moments he'll lose some matches.
"But at the same time he had a very negative draw against one of the best players in the world."
Nadal, gold medallist in the men's singles at Beijing 2008, beat Andreas Seppi 6-3 6-3 in the second round.
The 30-year-old, his nation's flag bearer at the opening ceremony, said there was no pressure on him.
"This is an event we only play every four years, so that makes the emotions even higher," Nadal said.
"I am enjoying on court, but at the same time not too much pressure for me.
"You know, [after] two months without competing I don't expect much. I just expect to enjoy the Olympic experience again and that's what I'm doing."