Who's lurking in London?

Rafa and Roger -- they're still the best two tennis players on the planet.

For the sixth straight year, they finished as the top two players in the ATP World Tour rankings. For the second time, Rafael Nadal reigns as the year-end No. 1-ranked player. No. 2 Roger Federer now has put together a record of eight consecutive seasons as either No. 1 or No. 2.

Nadal won seven titles, including the past three Grand Slam events. Federer won four titles, including the Australian Open. The rest of the top five? The trio of No. 3 Novak Djokovic, No. 4 Andy Murray and No. 5 Robin Soderling combined for zero majors and only five titles combined. That's quite a gap.

So what to expect at next week's Barclays ATP World Tour Finals, where all of the above will be joined by Tomas Berdych, David Ferrer and Andy Roddick?

"This," said ESPN analyst Darren Cahill, "could be the most competitive year-end event we've seen in years. Everybody's going in with great form."

The British oddsmakers favor Rafa slightly over Andy Murray and Federer.

Federer's current coach, Paul Annacone, was asked to rate Rafa's season.

"Anyone that wins three Grand Slam events in a year doesn't need much rating," Annacone wrote in an e-mail. "It really speaks for itself. The accomplishment is tremendous, and Rafa has done a super job being prepared to play and peaking at the major events."

The oddsmakers, however, seem to be discounting two things: (1) Nadal has won all of one indoor title in his entire career (Madrid, 2005), and the bounce-less carpet in London might be his least-favorite surface, and (2) there is no denying that among the eight competitors, Federer and Soderling come in with the most momentum.

Since losing in the quarterfinals at Wimbledon, the 29-year-old Federer is a sparkling 29-4 and has reached the final in five of his seven tournaments, losing in the U.S. Open semifinals to Djokovic and, last Sunday, the semifinals of the BNP Paribas Masters in Paris to Gael Monfils.

"It's obviously a beautiful moment," an emotional Federer said after winning his hometown tournament in Basel, Switzerland, for the fourth time, defeating Djokovic in the final. "I have to back it up [in London] now."

With Federer and Rafa in separate groups, the possibility of a meeting in the final is quite possible. Oddly, they have only met once in a year-end event, when Federer beat Nadal in straight sets in the Tennis Masters Cup in Shanghai in 2006. Federer's record at the year-end event is a shimmering 29-7.

Rafa leads the head-to-head rivalry by a lopsided 14-7, but …

• Twelve of those 21 matches came on Nadal's favorite surface (and Federer's least-favorite surface), clay, where Rafa holds a commanding 10-2 edge.

• In the other nine non-clay matches, Federer has a 5-4 edge.

• Incredibly, only one of Rafa's 43 career titles came indoors. Although he has a staggering record of 425-74 (.852) outdoors, he is a relatively pedestrian 43-26 (.623) on the inside.

"Rafa produced one of the greatest seasons ever," Cahill said. "He's going to Australia with a chance for the Rafa Slam. What he's done in last couple of years goes beyond what you can sum up in a few lines.

"Don't forget that Rafa has stepped up to every challenge so far in 2010."

When Nadal started winning French Open titles, some suspected he would never fully adapt to the grass at the All England Club. When he won his first title there in 2008, they were proved wrong. Some felt he would never master the hard surface in Melbourne, but he proved those cynics incorrect in 2009. The last obstacle was the U.S. Open. Rafa trimmed back his schedule and came into New York with more energy and hoisted the trophy. Who is to say, even after he withdrew from Paris with a tender left shoulder, that he won't solve the year-end void on his résumé?

The thing to remember about the ATP Finals is that surprise is always lurking. Federer won four of five year-enders between 2003 and 2007, but can you remember who won the one in the middle and -- not much easier to recall -- who took the title the past two years?

David Nalbandian, of all people, beat Federer in the 2005 final in Shanghai. In 2008, it was Novak Djokovic over Nikolay Davydenko in the final. In London's inaugural event, Davydenko took down Juan Martin del Potro. Davydenko's recent win over Tomas Berdych suggests a similar scenario is possible.

"So many times it goes down to who has enough in the tank to get in the trenches and compete well," said ESPN analyst Pam Shriver. "Playing indoors makes it tough for Rafa. Last year, he had nothing left -- a total disaster. There's no wind, so the guys like Federer, Berdych and Soderling come into the conversation. Look at what Davydenko did last year.

"I'd put Rafa second or third in the mix behind Federer. It's going to come down to one thing: At the end of the season, what's in the gut?"

Greg Garber is a senior writer for ESPN.com.