Djokovic in all-Serb clash, Federer, Tsonga through

Djokovic, who has lost just two matches in a spectacular season that has seen him win the Australian Open and Wimbledon as he surged to number one, defeated Alexandr Dolgopolov 7-6 (16/14), 6-4, 6-2 to advance to a last-eight meeting with friend and Davis Cup teammate Janko Tipsarevic.

Third-seeded Federer dismantled unseeded Argentinian Juan Monaco 6-1, 6-2, 6-0 to line up a clash with France's Tsonga, the man who rallied from two sets down to beat him in the Wimbledon quarter-finals.

Tsonga, the 11th seed, doused the hopes of eighth-seeded American Mardy Fish 6-4, 6-7 (5/7), 3-6, 6-4, 6-2.

Their three-hour, 43-minute tussle on the Arthur Ashe court helped ensure that Federer didn't take the court until shortly before midnight.

Federer and Monaco also had to wait out the protracted battle between women's world number one Caroline Wozniacki and former champion Svetlana Kuznetsova.

Once they had, a focused Federer appeared determined not to stay up any later than he had to.

He won the first set in 18 minutes and by the time it was all over he had blasted 42 winners -- including 14 aces -- past the hapless Monaco.

After breaking Monaco in the opening game of the second set, Federer won the next game with four straight aces.

"It's only a game, only a few points, but it's nice to win it that way," Federer said.

"It's tough for Juan," Federer said. "I've been in his position before. I thought he fought bravely. Sometimes it's not your time -- tonight it was mine."

Tsonga and Fish, in contrast, battled for almost four hours, both finding the going tough in the swirling afternoon winds.

"Today was just really difficult because of Mardy, of course, because of the wind, because of all the conditions," said Tsonga, who also beat Federer in Montreal in August.

For Fish, playing his first Grand Slam as America's top-ranked man, it was a bitter pill to swallow after a hardcourt victory and two finals appearances in the build-up to the US Open.

Djokovic, playing out on the smaller Louis Armstrong Stadium, also struggled with the wind and with the unpredictable Dolgopolov in the early going, needing six set points -- and saving four -- to claim the marathon first-set tiebreaker.

"I was confused on the court the first set," admitted Djokovic, who nevertheless notched his 61st match victory of the year with relative ease.

"I think it was exciting for the crowd to watch because it was very close," he said. "But I think it was game-wise an ugly first set because I wasn't happy with the way I played."

Ugly or not, the packed house loved it, and Djokovic said he was happy to play a match on the more intimate Armstrong court.

"Sometimes it's really nice to be on the smaller court where the crowd is closer to the court where you can feel them."

Two straight forehand errors from Djokovic gave Dolgopolov a 4-0 lead in the tiebreaker.

A favorable net cord helped Djokovic take the next point to launch a run of five straight, and he finally finished it off when Dolgopolov sent a forehand long.

From there Djokovic was in control, opening each of the next two sets with service breaks and rolling home from there.

Djokovic said it would be difficult to play Tipsarevic in the quarter-finals, but the match-up has an upside.

"There's going to be a Serbian in the semi-finals, which is great for our country," he said.

Tipsarevic, 27, reached the last eight of a Grand Slam for the first time, his 20 aces helping him prevail in a baseline battle against former world number one Juan Carlos Ferrero 7-5, 6-7 (3/7), 6-5, 6-2.

The quarter-final lineup will be completed on Tuesday, when defending champion and second seed Rafael Nadal takes on unseeded Gilles Muller of Luxembourg and world number four Andy Murray tackles young American Donald Young.

Fifth-seeded David Ferrer of Spain faces America's former world number one Andy Roddick, and French 12th seed Gilles Simon meets big-serving American John Isner.