Novak Djokovic and John McEnroe, bad boy clown princes from two different tennis eras, traded comic impressions of each other and even played a few points in an impromptu US Open moment Monday night.

To borrow 50-year-old McEnroe's famous 1980s catch phrase from his angry younger days, "You Cannot Be Serious" when two attention-grabbing entertainers played it for laughs on the Flushing Meadows hardcourts.

"Everyone has a different personality," Djokovic said. "1 like to entertain the crowd and that makes me happy in a way as well.

"What I ve done in 2007 with those impersonations and tonight playing with Johnny Mac, I think that's what the crowd wants, especially in these hours. I think these night matches are very special. "

The comedic spectacle at Arthur Ashe

Stadium came moments after Serbian fourth seed Djokovic defeated Czech Radek Stepanek 6-1, 6-3, 6-3 to book a place in the quarterfinals of the year's final Grand Slam.

Djokovic made famous his impersonations of such stars as Rafael Nadal and Maria Sharapova in 2007 and followed up by calling down McEnroe from a television commentary booth to come onto the court and play a few points.

"Johnny Mac made it all happen," Djokovic said. "It wasn't easy coming down in Jeans and a shirt but he made it all ftin."

Djokovic managed to mimic the mannerisms and serving style of McEnroe on the spur of the moment, pacing the baseline and hurling the ball high into the air before smacking it into the net.

He hurled his racket to the concrete and screamed at an imaginary umpire, channelling McEnroe's infamous rants to the delight of those who remained in the stands to the late-night finish.

"I didn't work at it at all. It just comes if the moment is right," Djokovic said. "It comes spontaneously and the moment

was right now. It was quite funny and the crowd loved it and that was the most important thing."

Once McEnroe arrived, having grabbed a well-used racket along the way, he unbuttoned his white shirt, rolled up his sleeves and began an imitation of the 2008 Australian Open champion.

McEnroe bounced the ball repeatedly low to the court, a good-natured dig back at Djokovic's pre-serve habits.

McEnroe managed to serve a few balls over the net, making a memorable forehand volley winner past Djokovic. A few comedic swings later, they met at the net and exchanged pats on the back as the crowd roared in delight.

McEnroe won three Wimbledon titles and four US Opens, including his last Grand Slam crown in 1984.

Djokovic will next face Spanish 10th seed Fernando Verdasco for a semifinal berth, possibly against five-time defending champion and world number one Roger Federer.

"If I play the way 1 did tonight, 1 feel like I can win against anybody," Djokovic said.