Melbourne - Former Australian Open runner-up Marin Cilic rolled back the years on Friday to outlast ninth seed Roberto Bautista Agut over five sets and book a spot in the round of 16.
The 31-year-old unseeded Croatian had a forgettable season last year, sliding down the rankings from seven to 39, his lowest year-ending position since 2007.
But he has started the season on fire and claimed a big scalp in beating the Spaniard, a Wimbledon semi-finalist last year, 6-7 (3-7), 6-4, 6-0, 5-7, 6-3 on Melbourne Arena.
"It was four hours of incredible tennis and unreal emotions," said Cilic, who won 11 games in a row at one point in what was his second five-set match on the trot.
"There was an incredible patch of surreal tennis where every ball was going in. But I knew Roberto would fight back.
"He pushed me all the way in the fourth set, but I had a great mindset in the fifth."
Cilic, whose career high was beating Roger Federer to win the US Open in 2014, is eyeing a deep run at the Australian Open.
He made the semi-finals at Melbourne Park in 2010 and lost to Federer in a five-set epic in the 2018 decider, after beating Rafael Nadal along the way.
Cilic's reward is a clash with Greek sixth seed Stefanos Tsitsipas or Canadian 32nd seed Milos Raonic for a place in the quarter-finals.