Andy Roddick broke his own fastest serve record as he helped the U.S. take a 2-0 lead over Belarus in their Davis Cup semi-final on Friday.

World number two Roddick overwhelmed Vladimir Voltchkov 6-1, 6-4, 6-4 in the opening match of the first tie between the two countries.

Olympic silver medallist Mardy Fish then defeated Max Mirnyi 7-5, 6-2, 3-6, 6-3 to give the U.S. a commanding lead.

The U.S. can reach the final for the first time since 1997 with victory in Saturday's doubles match or either of the two reverse singles.

Roddick broke his record with a 155mph (249kph) serve, two mph faster than the previous record, in the final game. He then closed the match with his 17th ace.

"I hit a good one," Roddick, who bowed to the crowd, said of the record-breaker.

"It's fun for the fans. For me, it's still a point. It is something I will be able to tell people one day," the American told reporters. "But I'm happier about the win and serving well overall."

That was especially true in the opening set when Roddick lost only one point on serve.

"I've practised many big times with another big server, but nothing like this," said Voltchkov.

Voltchkov, who has a sprained left wrist, had not played since the August Olympics and admitted he was very rusty.

"If it was somebody 15, 16 in the world, it would have been a little different," Voltchkov said. "But when you go to face a serve like that...."

BIG SERVE

Roddick said he wanted to set the tone of the match with his big serve in the first set.

"I was pleased that I was going to get out there first and hopefully get a 1-0 lead and maybe take a little pressure off Mardy Fish," Roddick said.

Roddick said he sensed Voltchkov was nervous in the first set and wanted to take advantage of that.

He did, winning the first three games before Voltchkov held serve.

"He was just making errors and wasn't making first serves in the first set, so I was thinking he was a little tight," Roddick said.

"I was trying to move him around a bit and he came up with some errors.

"I know I serve better than most guys on tour, but I just try to utilise that," he said. "I'm not worried so much about intimidating someone as I am beating someone."

Mirnyi said the opening-day scoreline was "the worst-case scenario for us", and Voltchkov all but announced he would play in the doubles on Saturday for Belarus, who are making their first appearance in the semi-finals.

"I think all of us here (can) read between the lines," Voltchkov said when asked whether he or teenager Alexander Skrypko would join Mirnyi in the doubles against U.S. twins Bob and Mike Bryan.

Either way, U.S. captain Patrick McEnroe appeared confident of victory.

"They (the Bryans) are a great team to have in there when you are looking to bring down the hammer," McEnroe said. "It is going to take a huge effort for Belarus to win the match."

France led hosts Spain 1-0 in a semi-final disrupted by bad light in Alicante.