Federer through as Roddick falls

Defending champion Roger Federer moved into round four of the US Open with victory over Lleyton Hewitt but Andy Roddick was knocked out by John Isner.

Top seed Federer came from behind to beat Hewitt 4-6 6-3 7-5 6-4 and will next play Tommy Robredo or James Blake.

But Roddick, seeded fifth, was stunned 6-3 7-6 (7-3) 6-3 3-6 5-7 7-6 (7-5) by unseeded fellow American Isner in a thriller lasting just over four hours.

Fourth seed Novak Djokovic battled to a four-set win against Jesse Witten.

Fernando Verdasco hit back from a break down in the final set to edge out German veteran Tommy Haas 3-6 7-5 7-6 (10-8) 1-6 6-4 and he will now play Isner.

Russia's Nikolay Davydenko, who is still yet to drop a set in the tournament, was made to work for his 6-4 7-5 7-5 win over world number 161 Marco Chiudinelli.

The eighth seed will face Robin Soderling in the fourth round after the Swede saw off American Sam Querrey 6-2 7-5 6-7 (6-8) 6-1.

Federer, the world number one, struggled to find a way past a scampering Hewitt in the early stages of the match and saw his break in the sixth game immediately wiped out by one from the Australian.

After facing down two break points in his next service game, Federer surrendered on a third to hand the first set to his 28-year-old opponent.

But Federer suddenly found his range to break Hewitt to love in the fourth game of the second set before holding his serve in similarly emphatic fashion to compound his advantage.

The pair were finally separated in a tight third set as Hewitt, who had lost the pair's previous 13 meetings, sent a slice long to allow Federer to edge ahead for the first time.

Hewitt fought bravely in the final set as he broke back at 5-2 down, but he could only delay his demise.

Federer, who committed 59 unforced errors in victory, admitted that he could easily have missed out on a a place in the last 16.

"It could have gone either way," he said. "He had a good start and he believed maybe more today than in some of the other ones he played against me.

"The way I came through, I was very happy, because I knew that being down a set against Lleyton is always going to be a difficult situation for me to be in.

"Make one more mistake and I'm in the fifth set maybe, or I go down completely. So I was relieved coming through."

Djokovic, who had not dropped a set in his first two matches, struggled in the heat before eventually claiming a 6-7 (2-7) 6-3 7-6 (7-2) 6-4 win over American qualifier Witten.

The gap of 272 ranking places between the two was hard to detect as Witten, who had beaten 29th seed Igor Andreev in the first round, took the first set on a tie-break.

Djokovic may have expected to cruise to victory after levelling in the second but, backed by a partisan crowd, Witten battled on to keep the Serb on court for almost three and a half hours.

"Looking at that match, I don't know who was number four in the world," said Djokovic said. "It was a tough win. For either one it would have been well deserved."

Witten, 26, who had not won a tour-level match before the event, is expected to rise around 100 places in the next set of rankings on the back of his performances.

"It gives me some money to keep playing. So now I can afford to keep playing for the rest of the year, at least," he said.

"I don't know how good I am, so it's good to kind of see that I can play with these guys and I kind of belong a little bit here."

Standing between Djokovic and a place in the quarter-finals is 15th seed Radek Stepanek, who also made heavy weather of his third-round match before eventually overcoming Philipp Kohlschreiber 4-6 6-2 6-3 6-3.