KEY BISCAYNE, Fla. -- Heading into Wednesday night's Sony Open tennis quarterfinal, this statistic loomed large: While Kei Nishikori was playing in only his 25th ATP World Tour Masters 1000 event, his opponent was looking for his 50th berth in a Masters semifinal.
That vast edge in experience would seem to suggest a Roger Federer victory, but tennis has a way of consistently delivering these May-October encounters in which the outcome is never certain.
And this one wasn't, not until the very end.
Nishikori, who was down a set and break in the second, came back to stun Federer 3-6, 7-5, 6-4.
One day after beating No. 4-ranked David Ferrer in a match that went longer than three hours, Nishikori backed it up with a win against the man many feel is the greatest player ever.
Federer's backhand failed him down the stretch and he finished with 39 unforced errors versus only 29 winners. Nishikori was more efficient, with 24 winners and 31 errors. In the end, the highest-ranked Japanese man (at No. 21) carved out one more break of serve (five) than Federer, who at 32 is eight years older.
Ultimately, Nishikori adapted to the conditions better, perhaps because he lives in Bradenton, Fla., which is less than 250 miles away. Federer said he worried too much about the wind.
"Just couldn't find my rhythm on the serve, which was surprising," Federer explained later. "Maybe the [cool, mid-60s] temperature had something to do with it. Haven't played that many matches in the dark. It's a bit frustrating, but Kei did well to stay with me. He was more consistent in the second and the third, which are the ones he won. To his credit.
"The second set just got away from me and the third was a tough battle. It was a tough end for me."
Nishikori did not seem intimidated; his career record against Federer is now 2-1. How many guys can say they're playing better than .500 ball against a 17-time Grand Slam champion?
"Yeah, it was second time to beat him," a low-key Nishikori said afterward. "I was hitting balls deep and striking well. And I was fighting."
With Federer serving at 4-3 in the second set, he broke to level the frame. And then, with Federer serving to reach a tiebreaker, the Swiss champion faded. A double fault and three errant backhands brought tidings of a third set.
There was a nice coming-of-age moment in the third game after Nishikori showed some nerves with a double fault and drew out his complaint to chair umpire Mohamed Lahyani to the extent that patrons began whistling. Standing at net, Nishikori had the temerity to smash the ball at the scuffling Federer, who actually got a racket on it. Nishikori got the point -- and a scowl to go with it -- and eventually held serve.
Perhaps coincidentally (or not), Nishikori fashioned a break point in the next game but pushed a backhand wide. Federer went on to hold. And then the good stuff happened.
At 4-all, Federer snuck into net and hit a forehand volley so delicate it might have evaporated before the ball boy got there. Nishikori responded with two terrific volleys of his own and took an on-serve lead of 5-4.
And here is how Nishikori won it:
First, he smoked a forehand winner, then Federer blew a makeable forehand approach shot to fall in a love-30 hole. An unreturnable wide forehand made it love-40. Federer managed to save two match points but the third skittered away from him when Nishikori, right leg hitched, pounded a backhand winner.
What's the difference this year?
"I think I am stepping more inside the court and serving well," Nishikori said. "Today I saved a lot of important points with my serve."
In his news conference, Federer predicted that Nishikori would soon be a top-10 player.
Federer, however, is still formidable.
With his recent finals appearance at Indian Wells, Federer has now reached at least one Masters final for 13 years running. Federer has collected an ATP-high 22 match wins; last year he won his 22nd match at Roland Garros -- in June.
"I mean, if I look at the big picture, since the beginning of the year, I'm very pleased with how I'm playing," Federer said. "So it's a good start to the season, no doubt. So I want to keep it up now for Geneva when I play next week, and then clearly we will shift over to the clay finally after a long stretch on the hard courts."
Nishikori, who is ranked No. 21 among ATP players, reached the fourth round of the Australian Open (losing to Rafael Nadal) and won the title at Memphis.
"Yeah, that was a great match," Nishikori said. "I was playing different tennis, I think, from that match against Rafa in Australia, step in more, aggressive like today. And, yeah, the game changed my tennis."
And he'll need his best, considering his semifinal opponent is Novak Djokovic.
"Yeah, he just won Indian Wells, and I guess he's playing well, no doubt," Nishikori said. "I don't know. I played him a long time ago, maybe three or four years ago in Basel, and, you know, I beat him before, so hopefully I can play good like today."