Novak Djokovic has left Roger Federer feeling a little worse for wear after crunching a forehand at his rival while they were playing doubles together.
They paired up for Team Europe against Team World on day one of the Laver Cup in Chicago, but suffered a 6-7, 6-3, 10-6 loss to Jack Sock and Kevin Anderson.
Djokovic put his head in his hands as soon as his shot struck Federer in the back, and had an embarrassed look on his face.
Both players saw the funny side of the situation, with Djokovic giving Federer's back a rub as the pair laughed about the incident.
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It was the first time Federer and Djokovic had teamed up in doubles.
Despite the defeat, which they suffered in the decisive match tie-breaker, Team Europe finished the first day with a 3-1 lead over Team World.
In the first match, Europe's Grigor Dimitrov prevailed 6-1, 6-4 over American Frances Tiafoe.
Watch Djokovic hit Federer in the video player below:
Great Britain's Kyle Edmund then secured a 6-4, 5-7, 10-6 victory over the USA's Sock.
The final singles battle saw David Goffin (Team Europe) edge out Diego Schwartzman (Team World) 6-4, 4-6, 11-9 in a thriller.
On day two of the competition, Federer will play singles against Australia's Nick Kyrgios, while Djokovic will face off against South Africa's Anderson.
Alexander Zverev (Team Europe) plays John Isner (Team World) in the other singles match.
In the doubles, Kyrgios and Sock will meet Goffin and Dimitrov.