The ATP World Tour Finals—the season-ending championship of men's tennis—begins on Sunday, November 9 in London. Over the next four days, we'll take a closer look at the seasons put forth so far by the eight singles competitors.

By the end of the 11-month tennis season, so much has happened that even one of its major champions can be forgotten. You can argue that such is the case with Wawrinka, whose Australian Open breakthrough seems like an eternity ago. Not only because it took place in January, but because he enters the World Tour Finals on a 1-4 slog, looking little like "The Man" who beat Nole and Rafa in Melbourne. But the Swiss can afford his late-year swoon because of his overall body of work. He won two other tournaments, including the Monte Carlo Masters with a win over Roger Federer, and reached the quarters at both Wimbledon and the U.S. Open. After a year in which Wawrinka came so close to a big win on so many occasions, his persistence finally paid off. Let's see if he can end 2014 as well as he started it.

Before an anti-climactic final-round win over an ailing Rafael Nadal, Wawrinka exorcised a heartbreaking five-set loss to Novak Djokovic at the 2013 Aussie Open in another overtime classic.

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Wawrinka also has the Davis Cup final coming up, but his losses in the Friday singles and Saturday doubles matches against Kazakhstan nearly derailed Switzerland's Cup quest back in April.

Wawrinka turns 30 next year and there's no guarantee he'll scale these heights again. He needs to rediscover his winning ways before the Davis Cup final and, equally as important, end his tour season on a high note.

ATP World Tour Finals Previews

November 5: Marin Cilic

November 5: Roger Federer  
November 6: Novak Djokovic  
November 6: Milos Raonic  
November 7: Andy Murray  
November 7: Stan Wawrinka  
November 8: Tomas Berdych  
November 8: Kei Nishikori