Powerhouse performances from Lleyton Hewitt and Sam Stosur kept Australia’s Hopman Cup title hopes alive at the expense of five-times winner the USA.

Dual grand slam winner Hewitt crushed world No.34 John Isner 6-1 7-5 in 75 minutes to give Australia an unassailable 2-0 lead in the Group A tie after world No.13 Sam Stosur cruised past Melanie Oudin 6-2 6-4 in 67 minutes earlier in the day.

However, the US won the mixed doubles 2-6 6-1 10-5 in a result that could affect Australia’s chances of reaching the final.

Tie-breaks in the Hopman Cup are won by the team or player who reaches 10 points first.

Top-seeded Australia, who suffered a shock 2-1 loss to Romania on Saturday, must now defeat Spain’s pairing of Tommy Robredo and Maria Jose Martinez Sanchez on Thursday to have any chance of topping the group.

This could be decided on countback if nations are equal on tie wins.

But it’s all over for the US, who lost their opening two ties and will be left playing for pride against Romania on Thursday.

World No.22 Hewitt was irresistible in the opening set of the men’s singles rubber as Isner’s booming serve abandoned him.

Hewitt never looked back after racing out to a 5-0 lead in the first set, although the American found some rhythm in a tightly contested second set.

“I played extremely well,” Hewitt said.

“John’s always going to be an awkward player for anyone.

“He’s pushed Federer before, he beat Roddick in five sets in a thrilling match at the US Open at the end of last year.

“I played him a couple of months ago (and beat him) so I kind of knew what to expect.

“He and Ivo Karlovic have a couple of the biggest serves in the game.

“I returned extremely well, made him play a lot of balls out there and really stepped up my game.”

Hewitt wore strapping on his right knee after jarring his leg in a three-set win over Victor Hanescu on Saturday.

But the former world No.1 said it was merely a precaution.

Stosur, who suffered a shock three-set loss to Romania’s Sorana Cirstea on the opening day of the tournament, said her win over world No.48 Oudin gave her a timely confidence boost in closing out matches after her recent fadeout against Cirstea.

“I thought I didn’t play too badly the other day, I just didn’t finish it off and today I definitely wanted to make sure that if I got that lead that I was able to close it out,” Stosur said.

“I think it’s all mental.

“It’s just one of those things.

“You’re playing a girl that’s got nothing to lose, who’s just going out there free hitting and swinging and before you know it you’re in a battle and the match is even again.

“I thought I played pretty well from the first point until the last point (today).”

© AAP 2012

Enjoy sports? Enjoy a bargain? All Sports Online has your favourite sporting brands at up to 70% off. Online only, premium quality sporting goods and merchandise at discounted prices. Get a deal now.