Tomas Berdych got on the board with a robin victory Wednesday at the season-ending $3.5 million ATP World Tour Finals.

The fifth-seeded Czech slugger improved to 1-1 this week by overcoming world No. 9 alternate Janko Tipsarevic 2-6, 6-3, 7-6 (8-6) in some Group A action on the indoor hardcourt at The O2 Arena. Berdych saved a match point at 5-6 in the third-set tiebreak and smacked nine aces before prevailing in just under 2 1/2 hours. Berdych also bested Tipsarevic at the Paris Masters two weeks ago.

This marked Tipsarevic's debut at this prestigious event. The capable Serb, who is the first alternate to play in this tournament since Radek Stepanek in 2008, dropped to 2-9 against top-10 competition this year.

Berdych, who lost to world No. 1 Novak Djokovic in a tough three-setter here on Monday, was last year's Wimbledon runner-up. Tipsarevic (0-1), who limped off the court after losing on Day 4, recently entered the top 10 for the first time in his career and joined the exclusive field here in London when world No. 3 and Australian Open runner-up Andy Murray (0-1) pulled out due to a groin injury.

The 6-foot-5 Berdych will face 5-foot-9 Spanish grinder David Ferrer here on Friday.

Wednesday's other Group A match will pit the high-flying Djokovic (1-0) against a seventh-seeded Ferrer (1-0), the 2007 runner-up at this lucrative event. The winner of that match is all but guaranteed a spot in Saturday's semifinals.

Djokovic is an incredible 70-4 this year, including Grand Slam titles at the U.S. Open, Wimbledon and Aussie Open. He was the Tour Finals champ three years ago.

Thursday's Group B round-robin bouts at The O2 will pit second-seeded Rafael Nadal (1-1) against sixth-seeded Jo-Wilfried Tsonga (1-1) and fourth-seeded and defending champion Roger Federer (2-0) versus eighth-seeded Mardy Fish (0-2), who has already been eliminated from semifinal contention. The five- time World Tour Finals titlist Federer dismantled his fellow former world No. 1 Nadal 6-3, 6-0 here on Tuesday.

The French Open runner-up Federer is already in the semis here, while the Nadal-Tsonga victor will join the super Swiss in the final four. Federer beat the French Open champion and Wimbledon and U.S. Open runner-up Nadal in last year's blockbuster Tour Finals finale.

This week's big winner will earn at least $770,000. An undefeated champion would pocket $1.63 million.