Bryans keep the US in the hunt for semis

Bob and Mike Bryan kept alive the United States's hopes of reaching the Davis Cup semi-finals with a 6-3, 6-1, 6-3 win over Croatian pair Roko Karanusic and Lovro Zovko in the doubles on Saturday.

The Bryan brothers had to win the doubles to extend the tie into a third day after the United States came off second best in Friday's epic singles matches, which had both gone to five sets.

"It's going to be a hard fought contest tomorrow... [to come come] back from losing 2-0," Mike Bryan told reporters.

"We're really happy we're back in this thing. We wanted to keep it short after they played for about nine hours yesterday. The guys believe we can actually win this tie, and that's the biggest thing."

The winner of the tie will face either the Czech Republic or 2008 finalists Argentina in the semi-finals in September.

Ivo Karlovic had been expected to play on Saturday but after his exhausting 3-1/2 hour win against James Blake on the opening day, Croatian captain Goran Prpic replaced him with Karanusic for the doubles.

The Americans were the first to break after a Zovko double fault gave them a 5-3 lead in the opening set. Bob served out the set to love.

The world number ones tightened their grip on the match by breaking in the third and fifth games of the second set before another double fault from Zovko ended the set 6-1.

The Bryans raced into a 4-1 lead in the third but the Croatians, cheered on by a partisan crowd, fought back to break the Americans for the first time in the match.

However, the Americans proved too strong and wrapped up the win in 68 minutes.

"It's never easy in the Davis Cup, we didn't know much about Karanusic, but we played like we played against the number one team in the world and it opened up for us," Bob told reporters.

Zovko added: "They are the best duo in the world, they play great together and you get very few chances to win points against them."

On Sunday, Marin Cilic will take on Blake in the first reverse singles and Karlovic is scheduled to face Mardy Fish in the final rubber.