Tim Henman went out of the Madrid Masters to Radek Stepanek in three sets despite finding something close to his best form.
The Czech won 6-4 1-6 6-3 after seeing off a fightback from Henman, who looked in pain late on but said afterwards that his suspect back was fine.
It was the second time in six days that Stepanek had beaten Henman, following his victory in Vienna last week.
Stepanek faces Argentina's Jose Acasuso in the last 16.
"It is a fair reflection because he has played a lot of games and got wins under his belt," said Henman after the defeat.
"The third set is a reflection of that, he was able to win and I wasn't.
"I think I am a better player than he is: I don't want that to sound flippant, but in the context of where I am at, I played some good tennis but came second and I am not going to dwell on it."
Henman looked to be heading for a quick defeat after dropping the first set but he held on from 15-40 in the first game of the second and raced through the set to level.
After struggling with a back injury for much of the year, Henman finally found some snap on his serve and the rest of his game clicked in to place.
The improvement was so sudden that, with the score at 5-0 in the second set, it was Stepanek who looked a beaten man as he received treatment on his back.
But the turnaround was only temporary and the Briton struggled to impose himself on the deciding set, constantly having to battle to hold serve.
Stepanek looked the likelier to break and so it proved when he moved 0-40 up in game eight, before Henman obliged with a wayward forehand on the second break point.
Henman appeared to wince in pain at one stage during the final game but he insisted afterwards that his recovery is on track.
"In terms of the way that I'm moving, the way that I'm feeling on the court, there is certainly a lot to be positive about," said the world number 26.
"In the context of this year, it's not the most important result of my career.
"I do feel a lot more enthusiastic and a lot more excited about my game because I'm out there playing pain-free. I've been able to play the way that I want to."
Henman is scheduled to play in Basel, Switzerland, next week.