London, England (SportsNetwork.com) - Former finalist Juan Martin del Potro and Swiss slugger Stanislas Wawrinka were Monday's round-robin winners at the $6 million ATP World Tour Finals.
The fourth-seeded del Potro was tested mightily by eighth seed Richard Gasquet before prevailing in the Day 1 nightcap, 6-7 (4-7), 6-3, 7-5, in 2 hours, 23 minutes. The tall Argentine broke for a 6-5 lead in the third set and then held his powerful serve to pickup the win.
"Delpo" broke Gasquet four times, while the nifty Frenchman settled for two breaks in his first Tour Finals match in six years.
The world No. 9 Gasquet corralled the final spot for this eight-man tournament last week. World No. 4 Andy Murray is missing the event after undergoing a recent back surgery.
Meanwhile, making his debut at this lucrative event, the seventh-seeded world No. 8 Wawrinka knocked off sixth-ranked Tomas Berdych 6-3, 6-7 (0-7), 6-3 in 2 hours, 25 minutes at the prestigious season-ending event at London's O2 Arena. The big-serving affair featured 27 aces, including 16 from the formidable Berdych.
Wawrinka broke the fifth-seeded Berdych on two occasions and held his serve throughout on Monday.
"My first impression was really, really nice to be here," Wawrinka said. "I saw that tournament so many times on TV. To win my first match here was something really special."
This week's four-player Group A features world No. 1 and U.S. and French Open champion Rafael Nadal, Roland Garros runner-up David Ferrer, the former Wimbledon finalist Berdych (0-1), and Wawrinka (1-0).
Group B is comprised of Australian Open titlist Novak Djokovic, the former U.S. Open champ del Potro (1-0), 17-time Grand Slam winner Roger Federer, and Gasquet (0-1). The two-time champion Djokovic was last year's big winner at The O2, beating the six-time Tour Finals champ Federer in the final.
Djokovic and Federer are the only former champions in this year's field. Nadal was the runner-up in 2010, Ferrer was the runner-up in 2007, and del Potro was a runner-up back in 2009.
The hot Djokovic beat Ferrer in last week's final at the Paris Masters and has won his last 17 matches overall.
On Tuesday, Nadal will battle his third-seeded fellow Spaniard Ferrer and the second-seeded Djokovic will take on his sixth-seeded fellow former No. 1 Federer.
Round-robin play will be staged through Saturday in London, with the semifinals on Sunday, and the final next Monday. The top-two players from each group will qualify for the semis.
An undefeated champion this week would earn $1.923 million.