Flushing Meadows shook with an explosion of deafening roars on Saturday as American sensations John Isner and Melanie Oudin sent former champions Andy Roddick and Maria Sharapova spinning out of the US Open.

On a day when Russian world number one Dinara Safina's luck and patience finally ran out in the third round, Isner and Oudin sparked off celebrations in their hometown of Georgia after showing off their "bulldog" spirit to full effect.

Big-serving Roddick came face-to-face with a 2.06-metre-tall (6-foot-9) player he had mentored up the ranks and as a way of thanks Isner boomed in 38 aces to trample the fifth seed 7-6 6-3 3-6 5-7 7-6.

"I'm happy for him. I'm mad that obviously it came at my expense," summed up Roddick who had hopes of going all the way this year following his runner-up finish at Wimbledon.

While 55th-ranked Isner was delighted to pull off the biggest shock of the men's draw, Oudin followed up her win over world number four Elena Dementieva by thumping another Russian.

The 17-year-old Oudin carved out a heart-pounding 3-6 6-4 7-5 win over 29th seed Sharapova.

As some 23,000 fans hollered inside Arthur Ashe Stadium, those who could not cram into centre court watched transfixed on the giant TV screen in the main fountain plaza.

When Oudin sealed the three-hour triumph by belting a forehand winner, spectators inside and outside the arena leapt to their feet to give her a standing ovation.

Oudin simply looked dazed as she dropped her racket before raising her weary arms to acknowledge the cheers.

"I just kept fighting as hard as I could. I can't believe it," the 70th-ranked Oudin gasped in a courtside interview as she tried to blink back tears.

"I just had a blast playing there today," added Oudin, who will aim to bump another Russian, Nadia Petrova, in the last 16.

Safina has long been famed for her fighting spirit and on many occasions has come from match point down to stifle her opponents.

But on Saturday, 72nd-ranked Czech teenager Petra Kvitova took a leaf out of Safina's Houdini manual and saved three match points before stamping her mark in New York with a 6-4 2-6 7-6 win.

A clearly irritated Safina then took a swipe at organisers for bumping her off the Ashe arena, where the day's schedule had over-run by almost three hours, and rescheduling her match to the smaller 10,000-seat Louis Armstrong Court.

"I'm number one player in the world, why did they move me?" asked Safina. "This is not an excuse but I don't think it's a fair decision they made."

As the women's field continued to be decimated - with no seed left in the top quarter - Isner finally burst the bubble in the men's draw as until his win over Roddick, it looked as if all 16 top seeds could reach the fourth round of a grand slam for the first time.

Earlier, five-times champion Roger Federer and world number four Novak Djokovic led a parade of seeds - Nikolay Davydenko (8), Fernando Verdasco (10), Robin Soderling (12), Tommy Robredo (14) and Radek Stepanek (15) - into the second week of the hardcourt major.

Federer, seeking a 16th major at Flushing Meadows, came into the match riding on a 13-match winning streak against Lleyton Hewitt but had to snap himself out of a lull to triumph 4-6 6-3 7-5 6-4.

Federer and Hewitt are two of just three fathers ranked in world's top 50 and it was the Swiss who was caught napping in the opening set, leading John McEnroe to quip: "Looks like he slept in the same room as the (six-week-old) twins last night."

But the scorching conditions and the Australian's inspired display, soon woke up Federer.

It was not long before Hewitt's role turned into that of an admiring spectator as the top seed flashed and flicked away an array of spell-binding winners to seal victory.

Serena through

Champion Serena Williams marched into quarter-finals yesterday with a ruthless 6-2 6-0 victory over 22nd seed Daniela Hantuchova of Slovakia.

The American broke twice in the first set and three times in the second to set up a quarter-final against either Russian seventh seed Vera Zvonareva or 10th seed Flavia Pennetta of Italy.

Other results: Nadal bt Almagro 7-5 6-4 6-4; Ferrero bt Simon 1-6 6-4 7-6 1-0 (Simon retired); Gonzalez bt Berdych 7-5 6-4 6-4.