Top seed Stefanos Tsitsipas made a shock exit from the Erste Bank Open as he was beaten by Frances Tiafoe in Vienna.
The American fought back from 3-0 down in the deciding set to secure a surprise 3-6 6-3 6-4 victory in an hour and 49 minutes on court.
A Tsitsipas double fault allowed Tiafoe to make the key break in the third set, and the pair have now won two each of their four meetings.
British number one Cameron Norrie squandered three match points as he was knocked out by Felix Auger-Aliassime.
It was a remarkable turnaround from sixth seed Auger-Aliassime, who was 3-6 down in the second-set tie-break before reeling off five points in a row to force a deciding set.
After two hours and 36 minutes, the Canadian came out on top with a 2-6 7-6 (6) 6-4 win and will face Alexander Zverev in the quarter-finals of the ATP 500 tournament.
Second seed Zverev and fourth seed Casper Ruud reached the last eight with wins over Alex De Minaur and Lorenzo Sonego respectively.
Diego Schwartzman, meanwhile, needed three sets to get past Gael Monfils, winning 7-6 (5) 4-6 6-2, and wildcard Dennis Novak was beaten 6-4 6-2 by Jannik Sinner.
Marin Cilic battled past home favourite Karen Khachanov in three sets to reach the quarter-finals at the St Petersburg Open.
The former world number three won 6-4 6-7 (1) 6-4, while third seed Roberto Bautista Agut triumphed in straight sets against Mackenzie McDonald, winning 6-3 6-2.
Qualifier Botic Van De Zandschulp booked his place in the next round with victory over eighth seed Sebastian Korda.
The Dutch 26-year-old, who reached the US Open quarter-finals, maintained his impressive recent form to win 6-2 7-5, while John Millman and Taylor Fritz also reached the last eight with straight-sets victories against Aslan Karatsev and Tommy Paul respectively.