Watch John McEnroe Join Pearl Jam Onstage For Neil Young Cover In London

Tennis legend John McEnroe went from spectator to performer this past weekend at London's Hyde Park when he donned a guitar and joined Pearl Jam onstage to play Neil Young's "Rockin' in the Free World."

Pearl Jam played through to the song's bridge before bringing out McEnroe to jam following Mike McCready's guitar solo.

"I think we need some help from Mr. Johnny Mac!" exclaimed frontman Eddie Vedder, as he led McEnroe to the front of the stage. "John McEnroe! Take that Wimbledon!"

McEnroe, who was sporting a Who T-shirt, immediately discarded his New York Yankees cap as he began strumming his Telecaster opposite guitarist Stone Gossard.

The tennis icon looked comfortable enough on the Hyde Park stage; just weeks earlier he performed "Already Gone" at the venue with the Eagles.

Check out fan-shot video of the performance via the player above!