The 24-year-old American, ranked 130 in the world, was not even meant to play the match.

Kozlov was training with the big star Rafael Nadal when he saw the messages on his phone.

He had been given a place in the main round of the Mexican Open as a "lucky loser" after another player resigned.

- Today I did not expect to play at all.

Now I have taken the biggest victory of my career and will face Rafael Nadal in the next round, says Kozlov according to ATP's website.

Suddenly, he was up against Grigor Dimitrov, the former world three, in the tournament and when he broke the opponent's serve to 2-1, he had a chance to take home the match in the next game.

But then he suffered a real cramp in his legs and could not hold it together.

But in the third set he scratched himself and ended up as the winner with 7-6, 5-7, 6-3 after a strong comeback.