Nishikori at Mexican Open

Nishikori at Mexican Open

ACAPULCO, Mexico - Japan's Kei Nishikori, 17th in the ATP rankings, plays a return in a men's singles first-round match against Albert Montanes of Spain at the Mexican Open tennis tournament in Acapulco, Mexico, on Feb. 28, 2012. Nishikori won the match to advance to the second round.

Nishikori retires in U.S. Open 3rd round

Nishikori retires in U.S. Open 3rd round

NEW YORK, United States - Japan's Kei Nishikori returns the ball during a third-round match at the U.S. Open against Spain's Albert Montanes on Sept. 4, 2010, at Billie Jean King National Tennis Center in New York. Nishikori suffered a groin injury and pulled out with Montanes leading.

Nishikori retires in U.S. Open 3rd round

Nishikori retires in U.S. Open 3rd round

NEW YORK, United States - Japan's Kei Nishikori returns the ball during a third-round match at the U.S. Open against Spain's Albert Montanes on Sept. 4, 2010, at Billie Jean King National Tennis Center in New York. Nishikori suffered a groin injury and pulled out with Montanes leading.

Nishikori retires in U.S. Open 3rd round

Nishikori retires in U.S. Open 3rd round

NEW YORK, United States - Japan's Kei Nishikori returns the ball during a third-round match at the U.S. Open against Spain's Albert Montanes on Sept. 4, 2010, at Billie Jean King National Tennis Center in New York. Nishikori suffered a groin injury and pulled out with Montanes leading. (Kyodo)

Nishikori retires in U.S. Open 3rd round

Nishikori retires in U.S. Open 3rd round

NEW YORK, United States - Japan's Kei Nishikori returns the ball during a third-round match at the U.S. Open against Spain's Albert Montanes on Sept. 4, 2010, at Billie Jean King National Tennis Center in New York. Nishikori suffered a groin injury and pulled out with Montanes leading. (Kyodo)

Nishikori at Mexican Open

Nishikori at Mexican Open

ACAPULCO, Mexico - Japan's Kei Nishikori, 17th in the ATP rankings, plays a return in a men's singles first-round match against Albert Montanes of Spain at the Mexican Open tennis tournament in Acapulco, Mexico, on Feb. 28, 2012. Nishikori won the match to advance to the second round. (Kyodo)