Britain's Kyle Edmund was left confused and frustrated after another bout of cramp dashed his hopes of reaching the second round of the Australian Open.
In baking hot conditions at Melbourne Park, Edmund twice led by a set against world number 81 Damir Dzumhur but cramp in his left leg helped the Bosnian fight back to win 1-6 7-6 (7/4) 4-6 6-3 6-1.
The British number three first called the trainer after the seventh game in the third set and while he managed to serve out for a 2-1 lead, it was one-way traffic thereafter.
Edmund suffered similar problems at the Davis Cup final in November when he led Belgium's David Goffin by two sets before cramp struck again.
"I'm disappointed with it obviously because it's not my tennis that's let me down because my tennis is good enough to do it, it's my body that's let me down," Edmund said.
"You can't play full out because you lose confidence in your movement and when you do move you start to cramp up again.
"It was the same situation I felt in Davis Cup where I couldn't do anything. To beat these guys you have to be 100 per cent. You can't play with your body cramping. It's frustrating."
The talented youngster from Yorkshire, ranked 88th in the world, was able to demonstrate his impressive striking ability during a glorious first set but this was only the third five-set match of his career and his body is yet to fully mature.
"I probably need to play more five-set matches but you can only play them when they come round," Edmund said.
"Hitting with Andy (Murray) for three hours, to cope you need to be in pretty decent nick and I can do that, day in day out. So it shouldn't be a reason why I'm cramping, but I am."
Murray, who has become something of a mentor for his compatriot, also struggled with cramp early in his career but has since developed into one of the fittest players on the tour.
"It's an option to speak to someone who has experienced this and come out the other side, who is physically robust now and doesn't really break down," Edmund said.
His potential is certainly not in doubt and he played like a dream in a 26-minute opening set, driving his forehand into the corners and breaking twice for the loss of just one game.
If the Briton was hoping for a swift work-out, however, he would soon be disappointed as Dzumhur found his rhythm to hit back and level at one set all.
Edmund broke early in the third but his momentum was halted at 4-3 when he first called on the trainer.
After a lengthy delay, he served out the set, but the pain was still causing trouble as the trainer again gave him treatment at the change of ends.
Wincing and clutching his knee, Edmund watched the next two sets sail by as the ruthless Dzumhur confirmed victory in three hours and 12 minutes.
"He is just 20 years old and he has such a good game," Dzumhur said. "I'm happy that I won against such a good player and in five sets so I am even happier."