"You don't win by just keeping the ball in play, " said Mats Wilander, who won three French Open titles.

WSJ: Rafael Nadal, the Underrated Tactician, Stalks Novak Djokovic

Safin's previous coaches include Mats Wilander, Peter Lundgren, Denis Golovanov and Marc Rosset.

BBC: Safin and Nalbandian hire coaches

"He hasn't quite figured out how to play five-set matches yet, " says Mats Wilander, the Swedish star who battled Mr. Lendl for years.

WSJ: Andy Murray Tries to Crack Tennis's Inner Circle

On April 10 at the Caesars Tennis Classic in Atlantic City he will play an exhibition match against former foe Mats Wilander.

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