Andy Roddick set a new serving speed record before powering the United States to a 2-0 lead over Austria on the opening day of their first-round Davis Cup World Group tie on Friday.

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The world number two dismantled Stefan Koubek 6-4, 6-4, 6-2 to give the Americans a huge advantage after Robby Ginepri had earlier battled back from two-sets down to beat Jurgen Melzer, 6-7, 4-6, 6-4, 6-4, 6-2.

Roddick, the 21-year-old U.S. Open champion, needed only 91 minutes to improve to 4-0 lifetime against Koubek in a match that included the fastest ever recorded serve of 150 mph.

The blast came on the American's first serve of the match and he equalled the feat later in the opening set.

The previous mark was held jointly by Roddick and Britain's Greg Rusedski at 149 mph.

With the victory, Roddick improved to 2-3 in Davis Cup play.

Despite setting the new mark, Roddick admitted that he was more concerned about his overall serving performance and the result for himself and the team.

"At the end of the day, the thing that matters is that I didn't get broken. And that's the one thing that I'll take any day," he said.

SURPRISE CHOICE

The 21-year-old Ginepri became the first American rookie to win a Davis Cup tie after falling two sets behind.

A surprise choice by U.S. captain Patrick McEnroe for the singles matches, Ginepri was struggling to justify his selection against the world number 76 before redeeming himself with victory on his first match point.

"I was so happy to get through," Ginepri told ESPN television.

"I was pretty nervous before but kept telling myself to stay calm. I always felt I could turn things around."

The American looked assured early on, racing to a 5-2 lead and holding a set point a game later on his own serve.

However, once Melzer had exposed Ginepri's brittle temperament to break back and force a tiebreak, the momentum changed drastically.

The left-hander took the breaker 8-6 on his fifth set point, before opening up a two-set lead by breaking in the 10th and final game of the second set.

Ginepri restored his confidence with an immediate break of serve in the third set and rarely looked back as Melzer became increasingly frustrated with his unforced errors and some inconsistent line calls.

McEnroe said: "Even at two sets down, I felt Robby could come back. He showed a lot of guts."

Ginepri had lost his only other career five-set match before Friday.

Saturday's doubles rubber features American duo Bob and Mike Bryan against Julian Knowle and Alexander Peya.

Victory for the Bryan twins, who are the world's top-ranked partnership, would clinch the opening-round encounter for the U.S. and set up a quarter-final showdown against the winner of the Australia-Sweden tie.