Medvedev was frustrated by 24-year-old Cressy's resistance, needing his ninth break point to finally take control of the fourth set and the match.

"I've played harder matches but this was long. It wasn't easy," he said.

"The fourth set was crazy. Every time I had a break point he would have second serves and hit the line. I couldn't return them."

The 25-year-old goes on to face Canadian ninth seed Felix Auger-Aliassime, who saw off 27th seed Marin Cilic of Croatia in his fourth-round match.

Auger-Aliassime, who knocked out Britain's Dan Evans in the previous round, won 2-6 7-6 (9-7) 6-2 7-6 (7-4).

Italian 11th seed Jannik Sinner also progressed, winning in straight sets against Australian 32nd seed Alex de Minaur to reach his first quarter-final in Melbourne.

The 20-year-old won 7-6 (7-3) 6-3 6-4 on Rod Laver Arena and will play Greek fourth seed Stefanos Tsitsipas or American 20th seed Taylor Fritz in the last eight.

Medvedev comes through 'most unlucky day of my life'

Medvedev, who won his maiden Grand Slam title at the US Open in September, is the highest seed in the men's singles because of Novak Djokovic's absence.

The Serb world number one was not allowed to play at Melbourne Park after he was deported from Australia because he was unvaccinated for Covid-19.

Medvedev dropped a set in his second-round match against home favourite Nick Kyrgios, but this battle against world number 70 Cressy left him even more frustrated.

Medvedev needed treatment on his right hip during the third set, with Cressy also later calling on the physio

After winning the first two sets, it seemed Medvedev was heading towards the quarter-finals when he led by a mini-break at 4-3 in the third-set tie-break.

But Cressy swung momentum back his way by winning both of the following points on Medvedev's serve.

The serve-and-volleying American put away a forehand at the net and then thumped a blistering winner past the Russian on his way to forcing a fourth set.

For the first time since the opening set, Medvedev forced a break point in a lengthy third game but was not able to take it as Cressy held on.

Medvedev's frustration began to show.

After shouting "this is so boring" before Cressy held for 2-1, the Russian complained at the changeover that his opponent was taking too long with his serves and claimed the 25-second shot clock was not being applied properly.

That annoyance was channelled into a 45-second hold to love, followed by creating three break opportunities for a 3-2 lead.

Cressy has won nine matches so far in 2022 and reached the first ATP final of his career in a warm-up event at Melbourne Park before the Grand Slam.

With Medvedev becoming increasingly rattled, Cressy showed why he has been successful by maintaining his composure and playing smartly.

Cressy survived two more break points in the seventh game, leading to Medvedev lamenting the "most unlucky day of his life".

But his pressure finally told in the 11th game when Medvedev decisively broke and served out victory in three hours and 30 minutes.