Ryan Sweeting made sure he didn't get too far ahead of himself in the U.S. Men's Clay Court Championship final — and ended up leaving Japanese star Kei Nishikori behind.

"I feel in the past I'd see the finish line and I'd start thinking about that," Sweeting said after beating Nishikori 6-4 7-6 (3) on Sunday for his first ATP World Tour title. "I didn't think about the end result today. In the tiebreaker, I just tried to play each point."

The 23-year-old Aerican became the fifth first-time winner on the ATP tour this year and the first U.S. Clay Court wild-card champion since Mardy Fish in 2006.

"I think I'm most happy the way I performed under pressure in my first final," Sweeting said. "I stayed calm and stayed focused. I didn't let the moment get to me which in past performances I have."

Sweeting, from Fort Lauderdale, Fla., turned pro in 2007 and had never reached an ATP semifinal until this week. He fell to the court in jubilation and fatigue after the hard-fought second set and later took a cannon ball victory dive into the River Oaks Country Club pool.

"There will be a celebration," Sweeting said. "It's on me."

Sweeting earned $80,650, and Nishikori took home $42,450.

Sweeting had to show his mettle even before the tiebreaker.

Trailing 5-4 in the second set, Sweeting served in the 10th game and had to overcome three set points before holding on a lob error by Nishikori that fell behind the line. The game lasted for 26 points.

"It was a good hold, it gave me a little bit of momentum going into the rest of the set and made it tougher on him," Sweeting said. "He's a competitor and he won't stop until the last point.

"He's very fit and I was a little fatigued after that game. I didn't want a third set."

The tiebreaker got tight when Sweeting double-faulted to bring the score to a 3-3 tie. Two errors by Nishikori and a forehand volley winner by Sweeting brought it to match point and it ended when Nishikori's forehand skipped wide.

Nishikori was trying to win the tournament to give inspiration to his tsunami-torn country.

Nishikori has a website that auctions donated items from players with all profit going to the tsunami victims in Japan. Items include a shoe worn by Maria Sharapova and a tennis racket signed by John McEnroe. A tennis shirt worn by Rafael Nadal at the Australian Open has surpassed $5,200 in bidding.

Nishikori almost pulled off a comeback late in the second set.

"I wasn't aggressive enough," Nishikori said. "I really wanted to win but I think he deserved it today. He played well, better."

Sweeting, the 2005 U.S. Open junior champion, entered the tournament ranked No. 93. The victory will kick his ranking up to about 71st.

Nishikori entered ranked 61st. His second-place finish will raise his ranking to about 49th. He is close to surpassing Shuzo Matsuoka, the highest-ranked Japanese player ever at No. 46 in 1992.

One year ago, Nishikori was unranked while recovering from elbow surgery in 2009.

"If I play well the rankings will come," Nishikori said. "I was struggling today, missing a lot and he was more aggressive than me. That's why I was struggling."