The two men played a record-breaking, 11-hour-five-minute match at Wimbledon last year and have since become good friends.

Isner showed he had endurance to match the speed of his serve as he came from 3-1 down to beat Potito Starace 7-6, 4-6, 6-4 and help the US to beat Italy 2-1 in the mixed-team Hopman Cup.

Mahut bounced back from the loss of his singles to world No. 4 Andy Murray with an inspirational performance in the mixed doubles as France defeated Britain by the same score.

The US now top Group B, in pole position to qualify for the final, though France and Italy can still finish ahead of them. Britain are the only team who cannot make the final.

Isner and Mahut will always be remembered for their Wimbledon encounter.

Isner, six feet nine inches (2.06 meters) tall, struggled in the hot and humid conditions in the Burswood Dome but bounced back from a loss of concentration at the start of the third set to win.

Bethanie Mattek-Sands had put the US ahead with a 6-4, 6-4 win over an out-of-sorts French Open Champion Francesca Schiavone. The Italians won the mixed doubles to salvage a point.

Mahut pushed Murray hard, getting two set points in the first set and another in the second but the Scot found his game when he needed it to clinch victory.

The French, who had taken the lead when Kristina Mladenovic beat Laura Robson 6-4, 3-6, 6-0, then outplayed the Britons in the mixed doubles to clinch victory

In Doha, second seed Roger Federer had to fight unusually hard for the second day in a succession before reaching the quarterfinals of the Qatar Open on Wednesday with a 7-6 (7/5), 7-5 win over compatriot and close friend Marco Chiudinelli.

The Grand Slam record-holder needed to recover from 4-5 down in the first set tie-breaker and from a break of serve down at 1-4 in the second set against his fellow Swiss, ranked only 117 in the world and who had to qualify for the main draw.

It followed Federer's knife-edge recovery in saving three successive set points in his opening encounter against Thomas Schoorel, the Dutch qualifier, before progressing similarly in two tight sets.

The cool conditions made it difficult for Federer to impose the heavier attacking game he is trying to accentuate in the later stages of his career, and it gave some of his efforts a labored look.

But he served well when it most mattered, and displayed his unique match instincts in digging himself out whenever he seemed to be sinking into difficult terrain.

It was also uncomfortable playing against a compatriot.

Federer next plays Viktor Troicki, a member of the Serbian team which won the Davis Cup in Belgrade last month and who reached the last eight with a 6-3, 6-1 win over Teimuraz Gabashvili of Russia.

Earlier Jo-Wilfried Tsonga continued his comeback from a knee injury by reaching the quarterfinals as well.

The former world No. 6 from France did that with an unusual finish in which two successful Hawkeye decisions in a row helped him to a 6-2, 6-4 win over Sergei Bubka, the son of Olympic gold medal pole vaulter Sergey Bubka.

"I think it's a good system - it brings justice," smiled Tsonga. "Before we had it, it was a bit difficult when you had to believe what the umpire said." Latvian fifth seed Ernests Gulbis dropped just five points on serve in a comprehensive 6-3, 6-1 win over Croatia qualifier Antonio Veic.

In Sydney, champion Andy Roddick weathered an early onslaught from hard-hitting Ukrainian Alexandr Dolgopolov before beating him 6-4, 6-1 to set up a quarterfinal clash with Marcos Baghdatis at the Brisbane International on Wednesday.

Fifth seed Baghdatis thumped Poland's Lukasz Kubot 6-2, 6-2 in just over an hour and was relishing the prospect of meeting Roddick on Thursday.

Sixth seed Feliciano Lopez, who had withdrawn from doubles event with a virus, had his singles campaign cut short as well after his 6-3, 6-1 defeat by unseeded South African Kevin Anderson.

In contrast, 2009 winner Stepanek, tamed fourth seed Mardy Fish 6-3, 6-1.

In the women's draw, Jelena Dokic, battling a wrist injury and a stomach virus, could not make the most of her wildcard and received a 6-0, 6-1 plastering from Germany's Andrea Petkovic before joining compatriots Stosur and Sally Peers on the sidelines.

In Chennai, India, top seed Tomas Berdych of the Czech Republic cruised into the quarterfinals of the $450,000 ATP Chennai Open with an easy win over Ivan Dodig on Wednesday.

The world number six trounced the 88th-ranked Croat 6-2, 6-4 in 87 minutes on the center court of the Nungambakkam Tennis Stadium in the southern Indian city.

Berdych, a first-timer in Chennai, beaten Frederico Gil of Portugal 6-0, 6-1 in just 45 minutes in Tuesday's opening round.

The Czech ace showed no signs of fatigue after taking the court for the second successive day as he broke Dodig twice in the first set and then again in the fifth game of the second set.