London Calling

This year's field at the ATP Championships is an interesting mix. Peppered with a mix of veterans and newbies -- relative or otherwise -- and plagued by injury, fatigue and some recent unexpected results, it might be harder to pick a favorite that you'd think. And it might open some holes just big enough to sneak through.

Group A
The first group of round robin matches is headlined by world #1 Novak Djokovic, who comes to London with a two-tournament (three, if you count the Davis Cup semis) losing streak -- something he hasn't had at any other time this year. He continues to struggle with a shoulder injury, and likely exhaustion, but he boasts the only winning record against the others in his group, and as the winner here three years ago, he certainly has the most experience.

For his first round robin match, Nole will play Tomas Berdych, appearing in London for the second straight time. The Czech, who really broke out in 2010, wasn't able to defend a lot of his points in the first half of the year, but picked the perfect time to play well again. He took the title in Beijing and beat three tough players to make the Paris semis. He's lost more than twice as many matches as he's won against the group, but if he's able to get an early jump on his opponents, he could cause damage.

Andy Murray had been riding one of the most successful streaks post-U.S. Open, winning three titles in Asia before losing to Berdych at the Paris Masters. Somewhat surprisingly, he has losing records against two of his three round robin groupies, but recent wins over Nole and his first opponent David Ferrer should give him confidence this week.

Ferrer can't be counted out, though. The veteran Spaniard is playing his third World Tour Final -- he was runner-up to Roger Federer in 2007 -- and has a fairly decent record against the guys he plays early this year. He hasn't won against any of these guys this year, but as one of the few in the field who hasn't been nursing injuries or illness the last few months, he could very well catch someone off guard.

Group B
Group B in London may be slightly more stacked with experience this year, but it's no less impenetrable. World #2 Rafael Nadal is the top seed, but he comes with significantly less momentum than he had this time last year. He hasn't won a title since Roland Garros and lost the last two finals he made. He pulled out of Paris to prep for this event, so hopefully he'll be well-rested, but with some tough challengers to contend with, it won't be smooth sailing.

Mardy Fish, playing in the post-season for the first time in his career, will open against Rafa. He'll be the underdog in London, for sure, but has notched some big upsets over the last two years -- including a win over Nadal in Cincinnati in August -- that should remind opponents he should not be overlooked. But his health remains a question mark -- a hamstring pull forced him to retire after one game in his first match in Basel and he wasn't able to hold on to a lead against Juan Monaco in Paris. It would be a shame if injury forced him to squander this opportunity, though, so I'm hoping the last week and a half gave him ample time to recover.

Defending champion Roger Federer is also in this group, and though he's fallen a few spots from the top he's having the most successful streak of anyone else in the field. Fresh off titles in Basel and Paris, he has a chance to prevent his least prolific year since 2002. Not counting Nadal, he has dominated his group-mates and might be in the perfect position to make a play for his record sixth championship.

But Jo-Wilfried Tsonga, who Roger's already played six times this year, might have something to say about that. The Frenchman, in just his second World Tour Final -- his first since 2008, staged a stunning comeback from two sets down to Federer in the Wimbledon quarters and repeated the win in Montreal about a month later. He's had a good fall, winning titles in Vienna and Metz, and though he lost in the Paris finals, he's arguably playing some of his best ball these days. He might be able to cause some real damage in his half of the draw.

With just a few days left before the first balls are struck at the year-end championships, players don't have a lot of time left to prepare. But even the biggest underdog should know everyone out there is beatable. And the one who's able to put the first dent in the field's armor could walk away with something huge.