LONDON (AP) -- Juan Martin del Potro got past Richard Gasquet to win his opening round-robin match at the ATP World Tour Finals on Monday.
Stanislas Wawrinka grabbed the spotlight with a win in his maiden appearance at the season-ending tournament.
After Wawrinka defeated Tomas Berdych 6-3, 6-7 (0), 6-3 in Group A, Del Potro beat Gasquet 6-7 (4), 6-3, 7-5 to secure crucial points in a tough Group B that also includes Roger Federer and Novak Djokovic, who will be facing off on Tuesday.
After the round-robin stage, the top two finishers in each group advance to the semifinals.
Playing in the tournament for the first time since 2007, Gasquet produced some stunning shots but struggled to return del Potro's big serve in a match laced with unforced errors and winners from both sides.
Gasquet said he was disappointed by the result, his sixth loss in seven matches against Del Potro, but took some comfort in the way he lost.
''The level is very high. So every match is a final for me,'' Gasquet said. ''Tonight I played well, I was really close.''
Del Potro, who hit 35 winners and made 40 unforced errors, was relieved to come out on top ahead of two difficult matches.
''This tournament means a lot to me,'' he said. ''In the end, I played solid and I won. Hopefully I can beat (Djokovic and Federer), but it's going to be really tough for me. I don't have anything to lose against them.''
Gasquet and Del Potro started their match with a 32-shot rally won by the Frenchman, who then comfortably held his serve at love. Del Potro answered with his trademark big winners and won his first three service games without dropping a point before Gasquet earned two break points in the eighth game and converted the second with a backhand down the line.
But Gasquet failed to build on the momentum as his opponent broke back immediately.
Both players traded brilliant shots in the tiebreaker, as Del Potro's clever drop shots and passing shots answered Gasquet's fine volleys. Gasquet's all-risk approach finally paid off as he sealed the set with two brilliant forehand winners.
In the second set, del Potro rallied from 40-0 down in the fourth game to break Gasquet's serve. He served out the set after Gasquet shanked an easy overhead that would have given him two break points in the ninth game.
In the decider, Del Potro broke for a 4-3 lead but wobbled at 5-4, offering three break points to his rival with a double fault and letting him back in the match by missing a volley.
Gasquet's resurgence was short-lived, though, as del Potro capitalized on the Frenchman's mistakes to break again immediately and then finish him off on his serve.
Stepping out of the shadow of Federer, Swiss No. 2 Wawrinka marked his first appearance at the tournament with a victory.
Wawrinka - the only first-time qualifier in this year's tournament - recovered from a slump in the second-set tiebreaker to win a contest that lasted nearly 2 1/2 hours, with the help of a large group of Swiss supporters.
''They wanted Roger and they had me,'' Wawrinka said. ''I'm not trying to compare myself with Roger. But I'm really, really happy we are both in the tournament. I think it's something really special for Switzerland. He's a really close friend. We're not in the same group, so we can really enjoy playing here together.''
Wawrinka and Berdych are in the same group as top-ranked Rafael Nadal and David Ferrer.
The 28-year-old Wawrinka served well throughout the match, hitting 11 aces and saving the five break points he faced.
Enjoying a season that saw him reach the semifinals at the U.S. Open, Wawrinka broke in the sixth game when Berdych sent a backhand wide. He then opened up a 5-2 lead before earning two set points on his serve with a forehand winner.
He showed nerves as he missed three consecutive easy shots to offer Berdych his first break point chance of the match, but raised his game at the right time and converted his fifth set point.
Wawrinka made several unforced errors in losing the second-set tiebreaker but recovered in the deciding set, breaking Berdych for a 3-1 lead and sealing the victory on his first match point.