Watch List: Roger Federer returns as race for No. 1 heats up in Shanghai

Roger Federer's No. 1 ranking is at stake this week in Shanghai. (Al Bello/Getty Images)

The Watch List spotlights the must-know storylines for the upcoming week in tennis. This week, the focus is on the ATP's Shanghai Masters.

• Shanghai Masters: The WTA took center stage the past two weeks with Tokyo and Beijing offering jam-packed fields and the subplot of qualification for the year-end championships. Now the spotlight belongs to the ATP, as the first of two fall Masters tournaments takes place in Shanghai. Despite security concerns and his own fatigue, Roger Federer is in the field and will be joined by Novak Djokovic and Andy Murray. The most notable players missing in action are No. 4 Rafael Nadal, who is still rehabbing his knees, No. 5 David Ferrer (illness) and No. 8 Juan Martin del Potro (wrist). Those absences mean that sixth-ranked Tomas Berdych is the fourth seed and No. 11 John Isner also received a first-round bye as the eighth seed.

Federer and Murray are in the same half, while Djokovic's half includes Berdych, Jo-Wilfried Tsonga and Janko Tipsarevic. Federer and Murray have fairly uncomplicated roads to the semifinals. The quarter to watch is Berdych's, where Japan Open champion Kei Nishikori is lurking (Nishikori defeated Berdych 7-5, 6-4 last week) along with Tokyo finalist Milos Raonic and China Open finalist Tsonga. That's a brutal quarter, with the winner likely to face Djokovic in the semifinals. Djokovic is coming off his third consecutive Beijing title.

Things to keep an eye on in Shanghai:

-- The race for No. 1: Federer's decision to play Shanghai, a tournament he's had no problems skipping in the past, is a blatant signal that he's gunning to finish the year No. 1. While Federer sits in the top spot now, a significant chunk of those points are based on his undefeated fall run last year, when he won Basel, Paris and the World Tour Finals. That's 3,000 points to defend over the next month or so. Outpacing Djokovic in Shanghai would do a lot in easing the pressure to replicate his 2011 indoor success. Federer can guarantee he'll stay No. 1 for at least another week if he makes the quarterfinals. If the Swiss fails to do so, then Djokovic could reclaim the No. 1 ranking by winning the tournament.

-- Murray momentum: The Brit looked great in Tokyo until the semifinal as Raonic saved two match points and won 6-3, 6-7 (5), 7-6 (4). Murray spent much of the week telling reporters that he was so focused on winning a Grand Slam event all these years that he couldn't get up for ATP tournaments. He said he wants that to change -- it has to if he ever wants to be No. 1 -- and that he doesn't want his summer momentum to stall. He hit a speed bump in Tokyo; let's see if he can get it right in Shanghai.

-- Race to London heats up: Four spots are still open for the ATP's World Tour Finals in London. With the Nos. 5 and 6 players sitting out this week (Ferrer and Del Potro), this is a great opportunity for Berdych, Tsonga, Tipsarevic and Nicolas Almagro to make a strong move toward qualification. Even Isner and Raonic have an outside chance for London. They're within 1,000 points of the No. 8 spot.

-- Americans in China: Isner took a much-needed three-week break after the U.S.' loss to Spain in the Davis Cup semifinals. Four of Isner's last seven matches have gone to a decisive final set, and the other three were grueling four-setters. Does he have enough in the tank mentally and physically to finish the year in the top 10?

-- Potential early matches to watch: Fernando Verdasco vs. Juan Monaco (second round); Sam Querrey vs. Kei Nishikori (second round); Andy Murray vs. Bernard Tomic (second round); John Isner vs. Richard Gasquet (third round); Jo-Wilfried Tsonga vs. Milos Raonic (third round); Tomas Berdych vs. Kei Nishikori (third round).

• Linz and Osaka: With the WTA Championships field set -- Victoria Azarenka, Maria Sharapova, Agnieszka Radwanska, Serena Williams, Petra Kvitova, Angelique Kerber, Sara Errani and Li Na are the eight qualifiers, with Sam Stosur and Marion Bartoli serving as alternates -- much of the late-season drama in the smaller tournaments is gone. But the field for the secondary year-end tournament in Sofia, Bulgaria, has yet to be finalized. The eight-player event includes the six highest-ranked winners of International series events (excluding those who make the WTA Championships) and two wild cards (Bulgaria's Tsvetana Pironkova and Maria Kirilenko).

Azarenka is still in the draw in Linz, Austria, though I'd be surprised to see her actually play through the tournament given her win in Beijing on Sunday. Otherwise, the tournament is full of players sputtering in their attempts to finish the season strong. Ana Ivanovic, Dominika Cibulkova, Lucie Safarova and a host of Germans (Sabine Lisicki, Julia Goerges and Andrea Petkovic) are in the draw.

In Osaka, Japan, the top-seeded Stosur will try to tighten up her game in advance of Istanbul. But look past Stosur and the draw is tremendously light (Laura Robson, ranked outside the top 50, is a seed). Christina McHale and Jamie Hampton lead the American women, and the field boasts a number of big names who've lost their consistency: Zheng Jie, Francesca Schiavone and Yaroslava Shvedova.

Hopman Cup: