NEW YORK – As Kei Nishikori contemplated becoming the first Japanese man to reach the U.S. Open's fourth round in the 40-year Open era, he kept repeating two phrases: "I was tired" and "I'm very happy."
Overcoming cramps that left his ankles, legs and back aching, the 126th-ranked Nishikori upset No. 4-seeded David Ferrer of Spain 6-4, 6-4, 3-6, 2-6, 7-5 Saturday night.
Only one other man from Japan reached the fourth round at any Grand Slam tournament in the Open era: Shuzo Matsuoka was a Wimbledon quarterfinalist in 1995.
"I'm very proud," Nishikori said.
The 18-year-old Nishikori is the youngest man to get this far at the U.S. Open since Marat Safin in 1998 — and the youngest man to beat one of the top-four seeded men in the hard-court major championship since a 17-year-old Bjorn Borg upset No. 3 Arthur Ashe in 1973.
Pretty heady company.
"I still can't believe it. I was playing great and he was playing great, too," Nishikori said during an on-court TV interview. "Biggest win for me."
That's for sure: Nishikori only had one other career victory over a top-20 player. That, though, came in the final of a hard-court tournament at Delray Beach, Fla., in February, when he beat James Blake.
There were significant milestones that day, too. Nishikori was the first Japanese man to win an ATP title since Matsuoka in 1992, and he was the youngest player from anywhere to win an ATP title since Lleyton Hewitt was 16 in 1998.
On Saturday, there was the matter of outlasting Ferrer, the man who eliminated Rafael Nadal at last year's U.S. Open en route to the semifinals.
Nishikori could have ended things earlier, but he wasted a two-set lead, then needed three match points to wrap up the victory. His first chance to end it came while serving for the match at 5-3 in the fifth set, but Ferrer came up with a backhand passing winner that caught the sideline. Ferrer eventually broke there.
Nishikori broke Ferrer in the final game, hitting a forehand winner down the line on the last point, before dropping his racket and flopping on his back.
Nishikori is playing in only his second career major tournament and knocked off No. 29 Juan Monaco in the first round.
"It's not a surprise," Ferrer said. "For sure, he will be a very good player, no?"