Andy Roddick out-muscled Russia's Marat Safin 7-6 7-6 on Thursday to win a battle of the heavy hitters and a place in the Masters Cup semi-finals.

There was little finesse on centre court at the Westside Tennis Club as the two giants traded thunderous serves and punishing groundstrokes for nearly two hours.

The victory pushed Roddick to the top of the Blue Group standings with a perfect 2-0 record. Safin slipped to 1-1, which means he needs to beat Britain's Tim Henman in their last round-robin match on Friday to qualify for the semi-finals.

Earlier, Henman crushed Argentina's Guillermo Coria 6-2 6-2 to keep alive his hopes of reaching the last four at the $4.45 million season finale and claiming his first title of the year.

The form player coming into Houston, with back-to-back Masters wins in Madrid and Paris, Safin could never gain the upper hand against Roddick, who has enjoyed a superb season and now has an ATP Tour-best 73 victories to his name.

"I felt I was lucky to get out of that first set but the rest of the match, I couldn't have asked for more," Roddick told reporters. "I came up big on the big points.

"I'm going to take a lot of positives out of these first two matches."

BOISTEROUS CROWD

Backed by a boisterous Texas crowd, Roddick took the early initiative by breaking Safin to pull ahead 4-2.

Safin broke back at 5-4 only to let the set slip away, losing the tiebreak 9-7 to the American.

There was little to separate the two men in the second set, Safin wasting chances to level the match when he failed to convert three set points.

When the volatile Russian sent a forehand sailing long to squander the last of his break opportunities, he exploded in a fit of anger, smashing his racket on to the ground and then snapping it across his knee.

The second set again came down to a racket-rattling tiebreak punctuated by six aces.

Roddick, owner of the world's fastest serve, went to his biggest weapon when he needed it most, blasting four of his 15 aces past Safin to take the tie-break 7-4, handing the Russian his fourth loss against 23 wins since the U.S. Open.

"I was just a little unlucky," said Safin after absorbing his third consecutive defeat at the hands of the American. "I've always said tiebreaks are a lottery.

"I had my chances, unfortunately today wasn't my day. But I'm still alive and I have a chance tomorrow against Tim."