Nick Kyrgios believes that staying cool against the "greatest of all time" was the reason behind his shock Madrid Open win over Roger Federer.

The Aussie edged out his Swiss counterpart 6-7 7-6 7-6 in a gruelling two-and-a-half-hour marathon in the Spanish capital to reach the third round today.

Victory was arguably more significant due to the fact that Federer has won 17 Grand Slam titles - and three Madrid Open crowns - but Krygios, 20, says that he was unmoved by the veteran's string of accolades.

"I think he's the greatest of all time. I knew before the match that I would have to play one of the greatest matches I have ever played, I wasn't intimidated at all," he told reporters.

"I have a lot of respect for him. It was just another tennis match, it was a chance to go out there and enjoy yourself and I happened to get the win."

Kyrgios had never reached the first round of the tournament until this year.