Juan Martin Del Potro lost to Nikolay Davydenko 6-3, 6-2 on Thursday in round-robin play at the Masters Cup. With both men entering the contest at 1-1 marks, the outcome decided which one would advance to the Shanghai semifinals. As a result, Davydenko moves on as the No. 2 seed out of the gold group behind Novak Djokovic, while Del Potro’s season ends.

Make that Del Potro’s regular season. He is key component of Argentina’s Davis Cup team, which will host Spain for the 2009 title the weekend after the Masters Cup. Del Potro was a perfect 2-0 in singles rubbers (with wins over Davydenko and Igor Andreev) during Argentina’s semifinal victory over Russia in September. His straight-set drubbing of Andreev came in a decisive fifth rubber.

After the Davis Cup final, it will be onwards and upwards to the Australian Open 2009 for Del Potro following, of course, a brief but well-deserved off-season.

As good as Del Potro was in 2008, question marks still hover over the 20-year-old heading into next year’s first Grand Slam. Del Potro started this season in relatively lackluster form before surging to four straight tournament titles in between Wimbledon and the U.S. Open. He did not lose a single match in that span. Still, the competition during that run was less than stellar. Del Potro beat Richard Gasquet in the Stuttgart final, but Gasquet suffered a mostly brutal 2008 campaign. In Kitzbuhel one week later, the best players Del Potro beat were Victor Hanescu and Jurgen Melzer. He took out Andy Roddick in the Los Angeles final, but Roddick was in miserable summer form until reaching the U.S. Open quarterfinals. Del Potro’s most impressive win in Washington, D.C. came over Tommy Haas in the semifinals, after which he went on to defeat Viktor Troicki in the title match. All in all, that’s some rather unimposing competition en route to four titles.

That brings us to the still-lingering question: can Del Potro produce similar results in Grand Slams and against the best players tennis has to offer? Can he beat the likes of Roger Federer, Rafael Nadal, Djokovic, and Andy Murray? Can he do it when the stage is bigger and the pressure higher?

We will find out at the upcoming Australian Open, but thus far the answer has been no. This year, Del Potro lost in the second round of the Australian Open (to David Ferrer), the French Open (to Simone Bolelli), and Wimbledon (to Stanislas Wawrinka). He reached the quarterfinals of the U.S. Open to cap off his awesome summer streak, but he almost lost to Gilles Simon in the third round (won 6-3 in the fifth set) and then bowed out to eventual runner-up Murray in the quarters. In 2007 he went out in the second round in Australia, first round of the French Open, second round at Wimbledon, and third round at the U.S. Open. A year earlier he lost in the first round of both the French and U.S. Opens. Sure, Del Potro is still just 20-years-old, but his Grand Slam history is nothing to write home about.

Will all of that change at the Australian Open 2009? It’s a definite possibility, as Del Potro has all the tools to hang with the big boys. He stands 6’6’’ and moves quite well for a man of the size. The No. 8 player in the world hits heavy groundstrokes off both wings and his backhand is especially rock-solid.

The scary thing about Del Potro is there is still a ton of room for improvement. His serve is good, but far from spectacular considering how tall he is. It can—and will—get better in a hurry. Furthermore, Del Potro does not like to come into net. With his size, wingspan, and big shots from the baseline, however, that is something he needs to do as often as possible. Once he adds a net game into his arsenal, he will be lethal.

Del Potro is coached by Franco Davin, who guided veteran Argentine Gaston Gaudio to a shocking Grand Slam title at the French Open in 2004. Will Davin be able to work similar magic with Del Potro? We will get a good idea of how hard they work during the off-season when Del Potro arrives at the Australian Open (although he is also scheduled to play the Heineken Open tune-up in order to get ready). Serves, volleys, and a slightly more consistent forehand should be tops on the to-do list between now and mid-January.

While the Grand Slam questions remain, with just a little improvement, Del Potro can be a major player at next season’s Australian Open.