Australian Open (day three): Dan Evans records biggest win of career over seventh seed Marin Cilic
Evans struggled with an eye problem early and lost the opening set but fought back to win in four sets 3-6, 7-5, 6-3, 6-3.
It is only the second time the 26-year-old has beaten a player ranked in the world's top ten.
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Hide AdThe British number three will now face either Bernard Tomic, of Australia, or Victor Estrella Burgos of the Dominican Republic in the third round.
Cilic, the 2014 US Open champion, took advantage of Evans' early struggles and breezed through the opening set in 31 minutes.
But the Brit responded in a tight second and forced the huge Croat into a string of errors to take it before a tie-break was required.
Evans, who beat Fabio Bagnis in round one on Monday, grew in confidence in the third set and, despite breaks of serve changing hands, he held his nerve to claim victory.
Evans has now reached the last 32 in three successive Grand Slam appearances -he also reached the third round of the US Open in 2013 – but he has never progressed to the last 16 stage.