Roger Federer's season ends with a loss to Rafael Nadal at the ATP Finals

Roger Federer's inconsistent season is over after a loss to the red-hot Rafael Nadal. (Anadolu Agency/Getty Images) LONDON -- Roger Federer's disappointing

Roger Federer's inconsistent season is over after a loss to the red-hot Rafael Nadal. (Anadolu Agency/Getty Images)

LONDON -- Roger Federer's disappointing season ended with a 7-5, 6-3 loss to Rafael Nadal in the semifinals of the ATP World Tour Finals on Sunday.

The match was a microcosm of Federer's season. There were flashes of brilliance and vintage shotmaking that made you think maybe he might finally get the big win he needs to turn the corner. But unforced errors abruptly ended many surges and, in a familiar pattern, he failed to close out points when he was ahead in the rally.

"I very rarely go through matches where I had no chance and no opportunities," Federer said. "This game is a game of making or missing your opportunities. Today was a little bit more of that, again. But I thought the margins were more on his side. He was playing more consistent. He was playing more solid. He plays the way he always plays. I just couldn't come up with the shots when I needed them, forehand or serve, moving forward."

Over the last four years, Federer's legendary rivalry with Nadal has fizzled. In their four meetings this year, Federer won only one set. The matchup hasn't been the same since Nadal's epic five-set victory on Federer's best surface, at the Wimbledon final in 2008.  That meeting, perhaps the greatest match ever played, was a watershed moment in both their careers, propelling Nadal into an all-court player while signaling that the Federer era of dominance was beginning to end.

Since that match, Nadal is 10-4 against Federer with five of those wins coming on hard courts, where Federer had traditionally held the edge. Nadal entered Sunday's match with an 0-4 record against Federer indoors, but now he's closed that gap as well.

Federer was once again the underdog, and while he tried to play relaxed and free with his shots, his consistency failed him. On a key break point at 2-3 in the first set, Federer had a forehand down the line all lined up for a winner and early lead. He fired it long by a yard. Though Federer fought back to break Nadal when he served for the set at 5-4, he continued to struggle off the ground. Federer finished with 17 winners to 32 unforced errors, while Nadal had 15 winners to 14 unforced errors.

"Maybe I shouldn't have [gone for it], but I did," he said. "No regrets there, I guess. I just struggled to stay consistent enough throughout the match, and that's why he deserved to win."

Nadal's first indoor win over Federer was as much about the Spaniard's improvement on the surface and his confidence after an incredible year of tennis, as it was about Federer's own struggles. Even in his prime, Federer had little success against Nadal's brand of topspin and defense -- Nadal now leads their head-to-head 22-10 -- and the Swiss admitted he's never felt settled when facing Nadal's lefty game.

"If you compare yesterday's match and today's match, it's like I have to play two different ways," said Federer, who beat Juan Martin del Potro on Saturday. "So for me it's much more of a change.  It's not an excuse. But I definitely have to play totally different. He can play pretty much the same like he plays against [Tomas] Berdych and Stan [Wawrinka], so forth.  It's definitely more up to me to getting used to the lefty spin quicker.  Coming over the return very often instead of chipping it, which I've been doing it all week."

"There's always going to be a bit of an up and down from that standpoint. But I thought it was OK at times. But just my court positioning, getting used to knowing exactly the dimension, how things are going to work out is sometimes a bit tricky. That's why I either chose the wrong side or I can't get the read I usually get like you get with del Potro, [Richard] Gasquet or [Novak] Djokovic for that matter."

Reflecting on his 2013 season, Federer said he's most pleased about his ability to finish it by playing three back-to-back tournaments without any major physical issues. He finished 4-10 against top-10 players, but three of those wins came in the last two weeks, a small nugget of positivity he can carry forward.

"I'm happy that I have that option, that I know I can play three weeks in a row because I remember [Andre] Agassi didn't do that at all any more toward the end of his career," he said. "He used to play one, maybe two, he would always pull out the third week if there was something planned. I was happy I was able to play Basel, Paris, here in London, through extremely tough conditions with a lot of running, tennis, traveling, so forth."

Federer has always been optimistic. Even after bad losses, he's been defiantly positive, a mindset has catapulted him to prolonged success. But it's a tour of winners, and Federer didn't win that much this year. He collected only one title, an ATP 250 in Halle, Germany, and he will close the season ranked outside the top five for the first time since 2002.

"If you look at the points difference from the points I'll make during this tournament and what the winner's going to make, it's like I never even played this tournament almost, which is fine," he said. "The winner deserves it all. It's very extreme. That's why when you don't win tournaments, you're not at the very, very top consistently, your ranking definitely starts slipping."

With that in mind, Federer says his goal next year isn't necessarily to win his 18th Grand Slam title or engage in a battle for the No. 1 ranking. He simply wants to win.

"Winning five titles or something [next year], something exciting, leaving the tournaments as winner," he said. "That's what keeps things exciting."

Federer won't expand or contract his schedule for next season, though the details are still being decided. But the fact that he's committing to what he calls "a full schedule" is a positive reflection on his outlook. Reporters didn't bring up retirement after his last match of the year, but Federer addressed the topic himself.