AP

CHICAGO (AP) — Roger Federer and Novak Djokovic looked quite comfortable while playing together for the first time Friday night.

Except for one particular point.

Djokovic drilled Federer in the lower back with a forehand in the third game of their doubles match against Kevin Anderson and Jack Sock in the Laver Cup. Djokovic covered his mouth with his left hand and leaned over after the ball went off his partner.

"I apologized right away," Djokovic said. "It didn't look that great."

Federer didn't seem to mind that much.

"To team up with somebody of his caliber is just a treat you know," he said.

Federer and Djokovic took the first set 7-6 in a tiebreaker, but Sock and Anderson won the second set 6-3 and then captured the deciding tiebreaker 10-6 to give Team World its lone win on the first day of the exhibition.

Federer and Djokovic last played against each other in the Cincinnati final on Aug. 19, when Djokovic won 6-4, 6-4 to become the player to claim all nine ATP Masters 1000 events since the series started in 1990. Djokovic leads the all-time series with 24 victories.

But the stars had never played on the same side of the net before Friday night at the United Center.

Federer, playing with a red racket, took the forehand side and Djokovic the backhand against the hard-serving Anderson and doubles standout Sock.

"It was a lot of fun. I want to thank Roger for playing with me," Djokovic said. "I loved it. Obviously I wanted to win as much as Roger. But those guys came up with some big shots."

Team Europe won the first three matches of the day. David Goffin edged Diego Schwartzman 6-4, 4-6, 11-9; Kyle Edmund beat Sock 6-4, 5-7, 10-6; and Grigor Dimitrov downed Frances Tiafoe 6-1, 6-4.