LONDON—Juan Martin Del Potro is by no means the favorite to win the ATP World Tour Finals, but after a standout fall and an impressive 6-7 (4), 6-3, 7-5 win over Richard Gasquet in his opening match in London, he certainly looks like a bona fide contender.

In scoring his sixth win in seven tries over the mercurial Frenchman, del Potro was the more advantageous player on the evening, withstanding various flashes of brilliance from Gasquet. He certainly had some notable hiccups, but not as many of the Gasquet, who fought hard but eventually could not withstand the Argentine’s relentless attack from inside the baseline.

The tower of Tandil has been physically fragile since he won the 2009 U.S. Open, undergoing right wrist surgery that sidelined him for most of 2010 and dealing with left wrist trouble this season, which left him unable to do much more with his backhand than slice it at the U.S. Open (where he lost in the second round).

But del Potro healed quickly after he left New York; this fall he won Tokyo, upset Rafael Nadal in the semifinals of Shanghai before losing to Novak Djokovic in a third-set tiebreaker, beat Roger Federer in the final of Basel, and reached the quarterfinals of last week’s Paris Masters, where Federer turned the tables on him.

Gasquet came out on fire at the O2 Arena Monday night, breaking Del Potro to 5-3 with a beautiful cross-court/down-the-line combination started by his famous one-handed backhand. But he failed to serve out the set and was broken to 5-5 when one of those backhands flew long. While the contest featured a number of colorful points, most rallies began with cross-court backhands, with Gasquet aiming to keep the ball away from del Potro’s fearsome forehand.

But Gasquet played a strong tiebreaker and ended it brilliantly, with a gorgeous drop shot, a forehand return-of-serve winner, and finally a smoking cross-court forehand.

Del Potro wasn't rattled and played a far better second set. Gasquet began to spray his shots, while his opponent moved more easily inside the court and dictated with his forehand.

The two went at it tooth and nail in the third set, occasionally mixing in net rushes. The court appears to be playing at medium speed, so there should be plenty of long rallies all week long.

Serving at 3-3, Gasquet fought off two break points with a leaping overhead and a cross-court backhand, but his one-hander failed him down break point, giving del Potro a 4-3 lead. But trying to serve the match out at 5-4, del Potro had a brain freeze of his own and was broken at love, ending the game with a double fault and backhand error.

Yet instead of seizing the opportunity, Gasquet gave the break right back when del Potro crushed a cross-court backhand winner to go up 6-5. Del Potro did not blink in his second chance to serve the match, banging a service winner to end the two-hour and 23-minute contest.

In the past 10 years at the ATP World Tour Finals, only two men outside of the Top 4 have won the title, the last being No. 7 Nikolay Davydenko in 2009. Del Potro, who resides in the difficult Group B along with Gasquet, Federer, and Djokovic, has a lot of work ahead of him, but he owns a 17-2 record since the U.S. Open. Being comfortable indoors with his huge game, he has more than an outside chance to be the third man to pull off the feat.