US Open 2011: Roger Federer beats Juan Monaco in early hours

Federer received a rapturous reception from the late-night New York crowd

Roger Federer wasted no time in beating Juan Monaco after the start of their US Open fourth-round match was delayed until approaching midnight in New York.

They had to wait for the preceding women's match to end and it was 2350 local time when five-time champion Federer struck the first ball.

The Swiss was in unstoppable form, winning 6-1 6-2 6-0 in just 82 minutes.

World number one Novak Djokovic earlier beat Ukrainian Alexandr Dolgopolov to reach the quarter-finals.

He is on course for a semi-final showdown with Federer, who appeared completely untroubled by the late start to his match with Argentine Monaco.

The five-time champion began in sparkling form, breaking twice in succession and serving out the first set in just 18 minutes.

Such was his dominance that at one point Federer hit four successive aces and with light rain falling in the third set, the 16-time Grand Slam champion stepped up the pace even more to wrap things up at 0113 local time.

The Swiss former world number one said he was accustomed to late starts.

"You have to be ready," he said.

"I knew I was going to play late and there were all kinds of possibilities that they might move us to another court. As tennis players we're used to it."

He also had sympathy for his opponent, who won only three games.

Federer added: "It's tough for Juan. I've been in that position before when I lost badly on this court to Andre Agassi, so I know what it feels like.

"Sometimes it's just not your day but it was mine tonight and it feels great."

Federer will next face 11th seed Jo-Wilfried Tsonga in a rematch of their Wimbledon quarter-final , which the Frenchman won from two sets down.

Tsonga defeated American eighth seed Mardy Fish 6-4 6-7 3-6 6-4 6-2 in a tense encounter on Arthur Ashe Stadium.

Djokovic saved four set points in an epic first set tie-break and needed six of his own on his way to a 7-6 (16-14) 6-4 6-2 win. He will next face compatriot Janko Tipsarevic, who beat Spain's Juan Carlos Ferrero 7-5 6-7 (3-7) 7-5 6-2.

Top-seed Djokovic racked up his 61st win in 63 matches this year but it was not without alarms, as Dolgopolov's unorthodox game caused him plenty of problems.

On a windy afternoon on Louis Armstrong Stadium, the 22nd seed kept Djokovic pinned back with his sliced backhand and, after the pair swapped breaks of serve, the first set went to a tie-break.

Dolgopolov was in total control at 4-0 up but then got unlucky with a net cord and Djokovic came racing back.

Each man would have their opportunities as the crowd reached fever pitch, with Dolgopolov playing one incredible point to see off a set point by picking up a drop shot that seemed impossible but, in the end, Djokovic converted his sixth break point and never looked back.

He broke at the start of the second and third sets to see out a straight-sets win that had been anything but straightforward for the first 75 minutes.

"Winning it was very important," Djokovic said of the tie-break. "That was probably the turning point. After that it was a good performance.

"He played a lot of low balls, slices - I was confused on the court. But it was really exciting."

Djokovic will now meet close friend and Davis Cup team-mate Tipsarevic for a place in the last four.

"It means there's going to be at least one Serbian in the semi-finals, which is great for our country," said Djokovic.

"I think this is the first time I play Janko in a Grand Slam. We are great friends. It's not going to be easy to play him, but look, it's the quarter-finals and we both want to win."

In the men's doubles, Britain's Jamie Delgado and Jonathan Marray could not join compatriots Colin Fleming and Ross Hutchins in the quarter-finals as they went down 6-7 (5-7) 6-2 6-3 to Polish sixth seeds Mariusz Fyrstenberg and Marcin Matkowski.