Fifth seed Juan Martin del Potro lost in five sets to Spain's Roberto Bautista Agut in the second round of the Australian Open.
Bautista Agut, the world No 62, twice came from a set down to prevail 4-6 6-3 5-7 6-4 7-5, sealing victory in three hours and 53 minutes shortly after 1am local time.
Del Potro won the warm-up tournament in Sydney last week but has now gone out early at the last two Grand Slams, having lost to Lleyton Hewitt in the second round of last year's US Open.
The Argentinean paid tribute to the performance of Bautista Agut, whose reward is a third-round meeting with 27th seed Benoit Paire.
Del Potro said: "I think he played a great match for the four hours. It's tough when someone plays at a very high level for four hours, tough to beat the opponent.
"I was close. But at every moment that I had a chance, he played an unbelievable shot.
"I think sometimes the favourites lose very early in a Grand Slam, like Federer at Wimbledon or Rafa, and then other ones at the US Open. Here it's my turn to get out very early in the tournament.
"But the season just started. I will try to be positive for the rest of the year."