Defending champion Lucas Pouille crashed out of the Hungarian Open after a shock straight-sets defeat by Australia's John Millman in the round of 16 on Thursday.
Millman, ranked 80 places above world number 14 Pouille, needed 73 minutes to clinch a 6-3, 6-4 victory and the best win of his career by ranking position.
"I'm really happy with how I played, how I stuck with it mentally... I took my chances well today," Millman said.
"I've come close a few times of late but couldn't quite get through, so a really good result, especially considering it's my first tournament on clay in a long time."
The 28-year-old Millman set up a quarter-final against Germany's Yannick Maden who overcame compatriot Maximilian Marterer 6-1, 6-3.
Fourth seed Denis Shapovalov also suffered an early exit as the 19-year-old Canadian was beaten 6-2, 6-4 by Georgia's Nikoloz Basilashvili.
Eighth seed Andreas Seppi powered past Russia's Mikhail Youzhny 6-1, 6-2 to reach the last eight.
Muguruza pulls out of Stuttgart event due to injury
World number three Garbine Muguruza was forced to retire with a back injury during her round of 16 match against Anastasia Pavlyuchenkova at the Stuttgart Open on Thursday.
Russian Pavlyuchenkova won the first set 7-5 before Spaniard Muguruza, the second seed, called it quits.
Caroline Garcia beat Ukrainian qualifier Marta Kostyuk 6-1, 3-6, 7-5 to book her place in the quarter-finals.
World number seven Garcia, who overcame Maria Sharapova in the first round, faced another stern test before taming the 15-year-old Kostyuk in one hour and 41 minutes.
"She plays great, moves well, and fights a lot on court. For me, it was a difficult match to prepare for, because I didn't know what to expect," Garcia said.
Kostyuk had advanced to the main draw by beating France's Alize Cornet and dumped out Antonia Lottner in the first round.
"There aren't many videos or stats on her because she's brand new on tour, so that's never easy. She just went for it," Garcia said.
Up next for Garcia is another Ukrainian in Elina Svitolina. The third seed was leading 2-6, 6-1, 3-2 when her opponent Marketa Vondrousova retired due to a thigh injury.
Former world number one Angelique Kerber was down a set and trailed by two games in the second against Estonia's Anett Kontaveit when she pulled out with a quad problem.
America's CoCo Vandeweghe battled past Laura Siegemund 6-4, 4-6, 6-3 to set up a last-eight showdown with top seed Simona Halep while Karolina Pliskova beat Veronika Kudermetova and next meets former French Open champion Jelena Ostapenko.