New York, Sep 6 (DPA) Roger Federer and Novak Dkjokovic overcame niggles to advance while fifth seed Andy Roddick fell to a defeat against a rising American to exit the US Open in a third-round heartbreak loss Saturday.

Top seed Federer recovered from a stuttering start to beat Lleyton Hewitt for the 14th time in succession, posting a 4-6, 6-3, 7-5, 6-4 win.

Djokovic, losing 2007 finalist to the Swiss and the fourth seed, battled to overcome American qualifier Jesse Witten 6-7 (2-7), 6-3, 7-6 (7-2), 6-4.

But Roddick, three times a losing Wimbledon finalist against Federer, was ambushed by countryman John Isner 7-6 (7-3), 6-3, 3-6, 5-7, 7-6 (7-5) to remain without a Grand Slam title since New York, 2003.

'It was a tough one to lose,' confessed Roddick, who made a comeback stand after trailing two sets to love.

'He was rolling the dice, that's the way he's most effective. That's the way he's going to make guys uncomfortable,' Roddick said of Isner, who served 38 aces to 20 for the seed

'Sitting back and just rallying, that's not going to work much for him. He's got to come out, make guys uncomfortable and just take people completely out of their rhythm.

'Being as big as he is (2.05 metres), he's certainly capable of doing that.'

Federer, aiming for a record sixth straight title at the event, had to struggle to maintain his grip on Hewitt, the 2001 Flushing Meadows champion.

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

Added Hewitt, who has not beaten Federer since 2003: 'I was pretty happy the way I played today.