Novak Djokovic was cursing the bad luck that left him playing Rafael Nadal "with one eye" at the Barclays ATP World Tour Finals in London.
The pair were locked in a titanic battle in front of an enthralled O2 Arena when Djokovic's right eye became irritated. The Serbian left the court at 4-4 to change his contact lens but he could not rectify the problem and succumbed to a 7-5 6-2 defeat.
Djokovic said: "I really feel sick talking about it, because it's just incredible that this happened to me. It never happened to me in my life. I felt great. I'm just really annoyed by the fact that something like this can really affect the match. I could not play. I could not see a ball, especially the return. It was just terrible. Playing with one eye is not enough, especially if you have Nadal across the net."
He added: "These things happen. Unfortunately, it happened in a very important match, in a very important moment. I will try to see a doctor and see if there is something more serious going on and in two days hopefully I can be ready."
The result, coupled with Tomas Berdych's 7-5 6-3 victory over Andy Roddick, means there is still all to play for in Group A, with Nadal on top of the table while Roddick remains in contention for a semi-final spot despite two defeats.
For Nadal, who repeated his US Open final win over Djokovic, it was a hugely welcome second victory on the court where he failed to win a set last year - even though the win did not come in the manner he would have wished.
"I'm very sorry for him," said the world number one. "For me it was a very important victory because my level was high again and I played very well, in the first set especially. It is a very important victory for the group because I am in a good position."
Nadal's only irritation came from a conversation with the umpire, who asked the 24-year-old to speed up between serves. It was far from an unfamiliar situation for the Spaniard, but he felt aggrieved given the circumstances.
"We have a very good relationship with Novak," said the Spaniard. "I think the (permitted) medical time-out is three minutes, not seven, like when he went to the toilet.
"If I wait seven minutes for him, and for me it isn't a problem, it shouldn't be a problem if I am five seconds late between points. That's what I said to him because he put me under pressure that I had to go faster."