by Matt Cronin, FOXSports.com

Comment

With world No. 1 Rafael Nadal missing the year-end Shanghai event because of right knee tendinitis, U.S. Open champion Roger Federer will be the favorite to defend his title. But Federer is no stone-cold lock to win his fifth crown at this tourney, as there are four men who could mount a serious challenge.

Roger Federer has his sights set on a fifth Masters Cup title. (Hamish Blair / Getty Images)

Here are the favorites, ranked from top to bottom, for the eight-man round robin, which begins Sunday:

1. Roger Federer

He saved his year with an astounding U.S. Open performance that brought him his 13th Grand Slam title. Federer has a remarkable 26-3 record at the Masters Cup, but outside of the U.S. Open this year, he hasn't won another major title. Taking this crown would solidify what has been an up-and-down year for the Swiss as he's struggled to overcome a lingering case of mono.

He loves hardcourts, which the Masters Cup is played on, as he combines aggressive all-around play with creative defense. But don't expect perfect play out of Federer, as his head is likely tilting toward the thought of winning record-tying Slam No. 14 at the Australian Open in January.

At the very least, he'll get pumped up for matches against Andy Murray — who has been rising very quickly and beat him in Madrid after losing to Federer in the U.S. Open final — and Novak Djokovic — who has slipped a bit but has conserved some energy for a big push in Shanghai.

Bottom line: If Federer serves and strikes his forehand as well as he can, title No. 5 should be his.

2. Andy Murray

He hasn't turned the Big 3 (Nadal, Federer and Djokovic) into the Big 4 yet, but with his second Masters Series crown in Madrid — where he outserved Federer in the semis — he's already convinced many of his countrymen that he's the second coming of Fred Perry. It's outside of Britain where he has to do the most convincing, but the world No. 4 has all the key ingredients to become a great player: smarts, grit and an abundance of talent.

3. Novak Djokovic

The Serbian has had a bit of a fade-out since the "worst moment" of his career at the U.S. Open, when he trash-talked the crowd after his victory over Andy Roddick, then fell miserably to Federer. But the strong-legged backboard is way too good to stay silent for too long, and this is the perfect venue (medium-speed hardcourts) for the Serb to pick up steam again.

4. Jo-Wilfried Tsonga

What a year it's been for the leaping 23-year-old Frenchman, who after an extraordinary run to the Australian Open final, re-injured his right knee in May and then was out for almost three months. But the serve-and-volleying sensation picked up a full head of steam in the fall and won his first Masters Series title in Paris when he bested a strong group that included Djokovic, Roddick, James Blake and David Nalbandian. Tsonga can serve big, crush his forehand and take over the net. He's a threat to anyone when he's zoning, and he's done that more often than not this year. He and Murray might transform the Big 3 into the Big 5 next year.

5. Andy Roddick

It hasn't been a great year for America's top player, who is without a Masters Series shield and failed to reach even a Grand Slam semifinal, but it's been a respectable season, with three smaller titles and some key wins over Federer, Nadal and Djokovic.

Andy Roddick has one last chance to make a splash in 2008. (Hamish Blair / Getty Images)

What Roddick hasn't done, however, is beat any of them at the Slams this year. While the gigantic server still competes hard enough to give himself shots at glory year after year, his talent level doesn't quite match up with the other super-elite players week after week.

6. Nikolay Davydenko

Outside of his extraordinary form in winning Miami, the Russian hasn't had a lot to write home about, with the exception of being exonerated after an exhaustive investigation for allegedly gambling on matches. Davydenko is fun to watch when he's skipping along and getting on top of the ball, but he could use a heavy dose of Marat Safin's fire at the Masters Cup, where's he's never advanced beyond the round-robin stage.

7. Juan Martin del Potro

After it appeared that he might not live up to his surefire top-five-to-be billing, the 20-year-old Argentine made his mark this summer, winning four titles while breaking into the top 10. The youngest player to earn a spot in Shanghai, Del Potro is tall, strong, moves well for his size and can hit strong it off both wings. With a little more seasoning and variety, he could become a top-5 fixture well into the next decade.

8. Gilles Simon

The Frenchman finished ninth in the race, but gained a late entry when Nadal pulled out. He's the weakest player of the bunch, but is steady, quick and has made the most of his talent, winning three titles and upsetting Nadal in Madrid. Simon is sure to play inspired tennis, but he's a little out of his element.