ATP World Tour Finals breakdown

The final eight are ready to do battle at the season-ending World Tour Finals this week in London. The field is divided into two round-robin groups, with the two most successful players from each group advancing to the semifinals. Group A consists of Rafael Nadal, David Ferrer, Tomas Berdych and Stanislas Wawrinka. Group B consists of Novak Djokovic, Juan Martin del Potro, Roger Federer and Richard Gasquet.

They're coming fresh -- or not-so-fresh -- off last week's Paris Masters, where all eight also made the quarterfinals. That means some familiar matchups are in store over the next few days. Four of the round-robin encounters will be rematches from last week. Here's how each looks entering the event.

Nadal Nadal

Rafael Nadal

Why he'll win: Who's won more than Nadal this season? The Spaniard has won a tour-leading 10 titles this season and has a 71-6 record since returning in February after a seven-month injury layoff. He's also been dominant on the hard courts (outdoors, anyway), and his head-to-head against the rest of the field at this event is 20-4 this year. If he plays the way he did against Richard Gasquet in the quarterfinals of Paris last week, it's hard to see anyone stopping him.

Why he won't: Where hasn't Nadal won so far in his career? This is one of the few places -- his best result was a final in 2010. There are no big reasons that can't change this year, but there are a few small ones. There's the time of year -- Nadal has only twice lifted a trophy after the US Open is over. There are the conditions -- Nadal has only once won a title indoors. And there's the location -- with his first-round loss at Wimbledon, Nadal is currently 0-1 in Britain. That last one isn't much to go on, but after the year he's had, the others will take what they can get.

His amazing season, however, may finally be starting to catch up to him. He's just 3-3 against the rest of the field since the US Open. Novak Djokovic, his biggest rival, looks much more comfortable at the moment, and the other players will also feel they have a better chance because of the quicker, lower-bouncing court and the struggles Nadal has had at this tournament. If he plays the way he did while losing to David Ferrer in the semifinals of Paris -- a day after beating Gasquet -- it's hard to see him lifting the trophy.

Djokovic Djokovic

Novak Djokovic

Why he'll win: Unlike Nadal, Djokovic tends to do well at this time of year and is coming in 17-0 since the US Open. He's also the defending champion at this event and is 15-4 against the rest of the tournament field this season. Perhaps most importantly, the Serb has also started turning the tables on Nadal. He's lost two of their three hard-court meetings this year, but won their last encounter in Beijing and should benefit from the indoor conditions at the O2 arena if the two meet again this week.

Why he won't: Winning is good, but it can also be tiring. Djokovic has racked up a lot of matches since the US Open, and has just a day off between playing the final in Paris and his first round-robin match. And his season doesn't even end there. Serbia takes on the Czech Republic in the Davis Cup final next week, and the patriotic Djokovic will want to be fit and prepared to play in front of his hometown crowds. There's also the slight prospect of taking the No. 1 ranking from Nadal to think about, though Djokovic says the chances are so small that he's more focused on gaining ground for next year. All this added pressure, together with all the matches he's played coming in, could start to have an effect as the week goes on.

Ferrer Ferrer

David Ferrer

Why he'll win: Everyone's got a chance, right? And those chances look a lot better after he defeated Nadal last week to score his biggest win of the season. His results had dropped off since reaching the French Open final, but last week's run suggests the 31-year-old may be ready for another charge. Though Ferrer is at his best on clay, he's shown his indoor credentials by winning the Paris Masters last year and reaching the final again this year, this time on the same surface that will be used in London. He makes players beat him, and outgrinding Ferrer isn't an easy ask at this point in a long and winding season.

Why he won't: This tournament is about beating top players, and that's Ferrer's sticking point. His record against everyone else at this event is 3-9 this season, and two of those wins -- Nadal and Berdych -- came last week. He's also worried about having less rest after reaching the final in Paris, noting that Nadal will have had one more day off when the two meet again in their first round-robin match. He has a shot at the semis after beating everyone in his round-robin group at some point during the season. But getting more wins against the field this week than he has all year? It's a tall order.

del Potro del Potro

Juan Martin del Potro

Why he'll win: When del Potro gets going, he and his gigantic forehand are tough to stop. Beating Djokovic, Andy Murray and then taking Nadal to three sets, as del Potro did in Indian Wells, may be the best showing by anyone this season apart from those three themselves. And the 2009 US Open champion has also been in good form recently, defeating Nadal in Shanghai and beating Federer to win Basel two weeks ago.

Why he won't: Del Potro may get going, but hasn't been able to keep going for very long. His Indian Wells was followed by an opening-round loss in Miami, not helped by some family distraction back home. A good run at Wimbledon and the hard-court season culminated in an early loss to Lleyton Hewitt at the US Open. He's played a lot of matches in the past two months, making fatigue a possible concern. And while on his way to London, del Potro had his personal belongings stolen, which again could leave him unsettled coming into this week.

Berdych Berdych

Tomas Berdych

Why he'll win: (Long pause.) Maybe he's saving his best for last? The Czech with big firepower has been underwhelming most of this year but did manage to lead the Czechs back to the Davis Cup final. With the tie against the Serbs coming up next week, maybe he can find inspiration a few days early. And if there's any advantage to losing in the first round of Basel and playing only three matches in Paris last week -- like Berdych, Gasquet and Wawrinka all did -- it's that they come in a bit more rested.

Why he won't: He's the only member of the top 10 not to win a title this year and is 2-10 against the rest of the field in London. Though he's got the game to beat anyone, Berdych hasn't capitalized on a lot of opportunities he's had this year, like playing a tired Djokovic in the Australian Open quarterfinals or facing a tired Nadal after beating Djokovic in the Rome quarterfinals. As a result, he doesn't seem confident enough to suddenly start scoring win after win against the top guys this week.

Federer Federer

Roger Federer

Why he'll win: After a tough season, he's finally starting to resemble his old self. Federer made the final of his hometown tournament in Basel two weeks ago, losing to del Potro, and then beat del Potro last week before losing his semifinal to Djokovic in three sets. In the process, the pieces of his game have begun coming together over the past week -- better movement, more consistent first serve, more effective returns. If he can keep that momentum going, the 17-time Grand Slam champ could quickly become very dangerous. He's won his event six times and the conditions at the O2 arena suit his game well.

Why he won't: Though Federer is playing better, he's still making uncharacteristic errors at important moments. That's a sign his confidence has not yet fully returned, and those types of mistakes are especially costly against the elite players. His win against del Potro in Paris last week was just his second top-10 win of the year (and the other came all the way back at the Australian Open), showing how far he's been from the upper reaches for most of the season.

Wawrinka Wawrinka

Stanislas Wawrinka

Why he'll win: Wawrinka has given Djokovic all he can handle at two Grand Slams this year, which means he can stay on the court with anyone at this point. Qualifying for his first Tour Finals has given him a big boost, and he should be able to play freely after exceeding his expectations for this season. Just like his more famous compatriot, Wawrinka struggles against Nadal and finds himself in the same round-robin group as the Spaniard. Still, he feels he might have a shot at beating the No.1 on this surface because Nadal's topspin won't trouble him as much.

Why he won't: Despite some big improvements, Wawrinka's season has still been more notable for good losses rather than good wins. His results have also tailed off since reaching the US Open semifinals, and he lost fairly tamely to Djokovic in Paris last week. He still struggles with self-belief on big occasions, and it's a big jump to now go and win this tournament.

Gasquet Gasquet

Richard Gasquet

Why he'll win: Gasquet is having arguably his best season yet, and certainly his best since 2007. His shot-making talent stands out even in this field, and he's now physically stronger and competing better. It's not unusual to see players now start hitting their stride at 27, and he could well be one of them.

Why he won't: He's scored some good wins against the likes of Ferrer and Berdych and won three small titles, but hasn't made a dent against Nadal or Djokovic (or Murray) when he's run into them. Going from that to winning most of his matches against the top eight this week? That's a long way away.