Rafael Nadal failed to convert three match points as he fell to a quarter-final defeat against Australian Jordan Thompson at the Brisbane International.
Nadal, 37, went close to sealing a straight-set victory but lost 5-7 7-6 (8-6) 6-3 to 29-year-old Thompson.
It was Nadal’s third match since returning to action after almost a year out with a hip injury.
Thompson will face world number 14 Grigor Dimitrov in the semi-finals on Saturday.
After wins over Dominic Thiem and Jason Kubler earlier this week, Nadal faced by far his toughest test yet of his comeback against Thompson, ranked 55th in the world.
Making his return to the tour ahead of the Australian Open, which he has won twice, Nadal dropped serve midway through the first set, only to respond with a break of his own immediately afterwards before accelerating away to take the opener.
Nadal, a 22-time grand slam winner, has fallen away to 672nd in the rankings during his period on the sidelines.
The former world number one may find plenty of positives from a tough workout, but he will know he should have chalked up another win. Chances to close out the match came his way in the tie-break, but Thompson clung on to force a deciding set.
Momentum was with the home player, and he soon broke the Nadal serve in the third set, with the veteran Spaniard this time proving unable to recover.
Bulgarian Dimitrov, who eliminated Andy Murray in the first round, will face Thompson in the semi-finals following a 6-1 6-4 quarter-final victory over Australian Rinky Hijikata.
The other semi-final on Saturday will see world number eight Holger Rune face Russian Roman Safiullin, after their respective quarter-final wins against James Duckworth and Matteo Arnaldi.