They are the tennis world's most celebrated couple. But when Andre Agassi and his wife Steffi Graf took to the courts on Sunday, they weren't so in synch: The game ended with three stitches for Graf after her husband inadvertently whacked her in the face with his tennis racket. It happened while the couple were rallying gently with two children during a fundraiser in Houston. Agassi, racket in his left hand, hit the ball and then struck his wife in the face as he followed through, the Associated Press reports. Graf put her left hand to her mouth after being struck, then walked off to the side of the court while Agassi followed to look after her. She was seen wiping her mouth with a towel before leaving the stadium. "She's Okay," Agassi told the AP. "It was an unfortunate accident." In an odd twist, the doctor who stitched up Graf's lip had paid $70,000 in an auction for a trip to Las Vegas to play tennis with the couple. Stefan Krenzer tended Graf's wound in the tennis club's training room, according to the Houston Chronicle. Agassi, 36 and Graf, 37, were in Houston for Agassi to participate in an Oprah Winfrey-sponsored reality show called The Big Give, the AP reports. Despite the accident, Agassi and Graf helped raise $225,000 for a local elementary school. Agassi retired from tennis in September after a stellar career including winning eight Grand Slam titles. Graf retired in 1999 with 22 Grand Slam titles. The couple have two children, Jaden, 5, and Jaz, 3, and live in Las Vegas.