Roger Federer is searching for a spot in his 12th straight ATP World Tour Finals. (Erick W. Rasco/SI)

While the U.S. Open may signal the end of the tennis season for some, there's still several tournaments to play, as the ATP and WTA tours move to Asia and then back to Europe for the final month and a half of the 2013 season.

Some players are chasing spots for the year-end championships (the top eight men and women qualify for their respective tournaments), which are both prestigious and lucrative opportunities. Other players are looking to shore up their rankings position for the next Grand Slam tournament, which is less than four months away.

Aside from those larger goals, there are ATP Masters events in Shanghai and Paris and WTA Premier-level events in Tokyo and Beijing, meaning there's a load of points on the line.

Here are the five men and women who need to dial in and finish the year strong:

ATP

Roger Federer (ATP Rank: No. 5, Race to London: No. 7): Federer is pursuing two things this fall: a spot in the ATP World Tour Finals and his confidence. Unfortunately, the former may be an easier task than the latter. He could drop to No. 8 in the Race to London, depending on Stanislas Wawrinka's performance at the Malaysian Open this weekend (and Richard Gasquet could come within 40 points of Federer if he wins the Thailand Open). However, Federer looks to be in good position to make the season-ending championships even if he finishes at No. 9 because Andy Murray could miss the finale after undergoing back surgery.

But let's set aside the fact that we're talking about Federer -- who has won the (unfortunately acronymed) WTFs a record six times and has qualified every year since 2002 -- merely playing in the event. Federer has an opportunity in the next few months to regroup and build some momentum going into 2014. Let's flash back to 2011, when Federer responded to a crushing loss to Novak Djokovic in the U.S. Open semifinals by closing the year on a 17-0 run and winning the Swiss Indoors, the Paris Masters and the World Tour Finals. Less than a year later, he won Wimbledon and reclaimed the No. 1 ranking.

John Isner (ATP Rank: No. 16, Race to London: No. 13): Isner is well aware of his complete futility outside the United States. Until he can start producing some consistent results overseas, he'll always hit a ceiling with respect to his ranking. It's somewhat understandable if Isner falters in the middle of the season, when the tour moves to clay and grass (though he's shown he can win on both surfaces), but he should be a force on the hard courts in Asia and indoor hard courts of Europe. A good run in both Shanghai and Paris would give him a huge boost heading into Australia next season, where he has virtually no points to defend.

David Ferrer (ATP Rank: No. 4, Race to London: No. 4): Still ranked No. 4 (and he'll rise to No. 3 temporarily soon because of Murray's absence), Ferrer has a whopping 1,900 points to defend over the next five weeks, including titles at the Valencia Open and Paris Masters. The big question for Ferrer -- who has struggled at tour events this summer -- is whether he can keep his ranking up in order to earn a top four seed at the Australian Open.

Tomas Berdych (ATP Rank: No. 6, Race to London: No. 5): With Ferrer having to defend a lot of points at a time when he hasn't been playing his best, the Czech has a chance to crack the top four and avoid having to face Djokovic, Rafael Nadal or Murray before the semifinals of the Australian Open. Berdych has semifinal points to defend in Shanghai and quarterfinal points in Paris.

Juan Martin del Potro (ATP Rank: No. 7, Race to London: No. 6): The Argentine says his wrist is feeling much better, so much better that he's taken a wild card into next week's Japan Open. Del Potro is in the same boat as Berdych in terms of the chase for the No. 4 spot. He doesn't have a load of points to defend at the Paris Masters (only 90), but he is the defending champion at Federer's hometown tournament in Basel.

WTA

Sloane Stephens (WTA Rank: No. 13/Race to Istanbul: No. 11): Stephens has a good chance of breaking into the top 10 for the first time and an outside shot at qualifying for the WTA Championships. But she suffered a setback in her bid to qualify for Istanbul with a second-round loss to Eugenie Bouchard at the Pan Pacific Open this week. Angelique Kerber's run to the final didn't help, either, as it allows the German to leapfrog Stephens in the Race rankings.

With no points to defend until next season, Stephens has redone her schedule to play a heavy slate of tournaments to end the season. Stephens, who has yet to make a WTA final, should have title opportunities at the Generali Ladies Linz and Luxembourg Open. As Stephens said at the U.S. Open, "If I don't [crack the top 10], then shame on me."

Petra Kvitova (WTA Rank: No. 11/Race to Istanbul: No. 7): After falling out of the top 10 for the first time since the beginning of 2011, Kvitova needs to use this last month of the season to right the ship. She's already shown some progress on that front by beating Venus Williams to make the final in Tokyo. That run puts her in a good position to qualify for the WTA Championships, which will put her back under a roof, where she plays her best tennis (she's also scheduled to play Linz and the Kremlin Cup in Moscow, which are also indoors). If she can find her form and dominate the indoors the way she's done in the past -- remember her 27-match indoor winning streak from 2011-12? -- she sets herself up well for next season.

Venus Williams (WTA Rank: No. 63): I was admittedly surprised to see Venus still in the Pan Pacific Open draw after Serena announced her withdrawal last week, but I was even more surprised by how well she played to make the semifinals. After struggling with her movement and serve for most of the year, Venus showed more than a few glimpses of her vintage form in Tokyo, and her body was able to grind through three tough three-set matches in three days (though she lost the third). This week's run will put her back in the top 40 on Monday, meaning she's well within shouting distance of securing a seeding at the Australian Open if she can crack the top 32. That would be huge for her and the field. No one wants to see Venus Williams as a dangerous floater at a Slam.

Caroline Wozniacki (WTA Rank: No. 8, Race to Istanbul: No. 14): How is Wozniacki's ranking outpacing her Race position? Because she tore through the fall season last year and has 1,340 points to defend the rest of the season -- more than a third of her overall total. The upshot is this: If Wozniacki doesn't have a good fall season, she risks finishing the season ranked outside the top 10 for the first time since 2008.

Laura Robson (WTA Rank: No. 38), Eugenie Bouchard (No. 46), Madison Keys (No. 43) and Monica Puig (No. 44)