Novak Djokovic's bid for tennis history at the US Open got off to a bumpy start against 18-year-old Danish qualifier Holger Rune.
The world No 1, bidding for a fourth Flushing Meadows title and to become the first man to complete the calendar Grand Slam in 52 years, dropped the second set against the spirited Rune.
However, the youngster began cramping up in the third and was in no fit state to mount a further challenge as Djokovic completed a 6-1, 6-7 (5), 6-2, 6-1 victory.
Novak Djokovic survived a scare in the US Open first round but won 6-1, 6-7 (5), 6-2, 6-1
Danish qualifier Holger Rune, 18, won the second set against the world No 1 on Wednesday
'I got to say it's never nice to finish a match like that. Holger deserves a big round of applause. It's unfortunate,' said Djokovic.
'I was trying to feel the ball out there. It wasn't the best of my performance but he played well and I didn't serve well in the decisive moments of the second set. After that it's difficult to talk about the match, he couldn't move much.
'It happened to me when I was younger. These things happen. You could see he struggled a lot and I feel for him. I'm sure we'll see a lot of him in the future.'
Djokovic, 34, was playing his first match since missing out on a bronze medal at the Olympics, and there was no initial sign of rust as he immediately broke Rune's serve and raced away with the first set in 26 minutes.
However Rune, swinging like the carefree, precocious teenager he probably is, broke Djokovic to love at the start of the second and had the Serbian rattled as he took the tie-break to level the match.
It was a curious set from Djokovic, with five double faults and 15 unforced errors telling
