Berdych admitted he had been paralyzed by nerves on his Tour Finals debut on Monday when Novak Djokovic brushed aside the Czech sixth seed in straight sets.

But, after overpowering eighth seed Roddick, the 25-year-old will go into his final Group A match against Rafael Nadal on Friday knowing a win would likely secure him a spot in the last four of the prestigious end-of-year tournament at London's O2 Arena.

Berdych is the only player among the eight here not to have won an ATP title this season, but the last time he played in London he defeated Roger Federer en route to the Wimbledon final.

The 25-year-old's fairytale run came to an end in the final against Nadal and his form has dipped dramatically since then, so this victory offers a last chance to end the year on a high.

Roddick had given a good account of himself against Nadal on Monday, serving 18 aces and even holding a break in the final set, before eventually succumbing to the world number one's relentless aggression.

Victories in his last four meetings with Berdych, including a success in the final of the Miami Masters this year, would have given Roddick further cause for encouragement.

But, like Roddick, Berdych is no slouch when it comes to peppering opponents with big serves and there were only two break points in the first 10 games.

Both fell to Roddick as Berdych served to stay in the set. Unfortunately for the former US Open champion, Berdych held his nerve impressively to escape from that precarious position.

Roddick seemed tentative when he served after that missed opportunity and Berdych took full advantage to earn a break point which he converted by curling a forehand winner down the line for a 6-5 lead.

After scrapping to stay in the match for long periods, Berdych suddenly looked full of confidence as he comfortably served out the set.

Roddick turned the air blue with some choice cursing as the set slipped away and he was grumbling again in the fifth game of the second set.

At break point on his serve, Roddick attempted an overhead shot from the back of the court that he believed clipped the line for winner even though it was called out.

He challenged the decision only to discover to his chagrin that the ball was indeed just wide, giving Berdych a break for a 3-2 lead and prompting Roddick to smash his racquet against his foot in frustration.

That triggered a complete meltdown from Roddick as the American skewed a series of shots wildly off-target, allowing Berdych to break again and clinch a surprise win.

On Tuesday, Roger Federer stretched his record to 2-0 by beating Andy Murray 6-4, 6-2 in Group B, and Robin Soderling defeated David Ferrer 7-5, 7-5. All four can still advance after Thursday’s final round-robin matches. In doubles, Wesley Moodie of South Africa and Dick Norman of Belgium beat Lukasz Kubot of Poland and Oliver Marach of Austria 6-1, 6-3.