Watch: Andre Agassi literally relied on Boris Becker's slip of tongue to read his serve

In the late 80s, there was new rivalry blooming in tennis as Andre Agassi and Boris Becker were dominating the tennis court. The German, though, dominated Agassi for the first three years the two faced each other.

Between 1988 and 1989, the pair met three times. In each instance, it was Becker who came on top. It was Becker’s serve that was considered to be the differentiating factor. As the competition grew so did Agassi’s drive to break Becker’s serve and snap his winless run against the German.

In the end the breakthrough came after the American noticed a small tick when Becker took serve.

Agassi said he spent endless hours watching tapes of Becker’s game, and soon he noticed the German’s tongue and how he would stick it out of his mouth just before tossing the ball for a serve. If it went to the left of his mouth he was serving wide towards the tramlines, if it remained in the middle the ball was staying central.

“I didn’t have a problem breaking his serve, I had a problem hiding the fact I could break it at will, I just didn’t want him keeping that tongue in his mouth,” Agassi said. “I told Boris after he retired. I told him at Oktoberfest, while we were having a pint. He fell off the chair. He said, ‘I used to go home and tell my wife – it’s like he reads my mind. Little did I know you were just reading my tongue’.”