Andy Murray struggled in the heat as he lost to Mardy Fish in the quarter-final of the Cincinnati Masters.
The Scot was visibly suffering in the second set, and also received treatment on an apparent knee problem, as Fish came through an energy-sapping contest 6-7 (7/9) 6-1 7-6 (7/5) in two hours 56 minutes.
Murray looked out on his feet at times between points in the third set but did not hold back during them before finally bowing out of the tournament.
It took until 5-5 in the first set for the first break points of the match to arrive, and they fell to Murray.
Fish saved them both as the set went into a tie-break, the Scot saving two set points before finally clinching it.
The world number four, though, looked a different player in the second set as injury and the heat of the day appeared to take their toll.
The American raced into a 4-0 lead, Murray feeling his knee in the second game and then apparently complaining of dizziness at the change of ends after the third game.
The 23-year-old got on the board in the set to make it 4-1. Fish rattled through the next two games to level the match.
Murray, though, saved two break points to prevent Fish taking a 2-0 lead.
He then forced a host of deuces on the Fish serve before the American managed to move 3-2 in front, eventually taking the decider into another tie-break. Murray moved 4-2 ahead but a successful challenge gave Fish the advantage at 5-4 and the American closed out the match.
Meanwhile, world number one Serena Williams has pulled out of the US Open as she continues to recover from a cut to her right foot.