Defending champion Daniil Medvedev been sent packing at the St Petersburg Open after Reilly Opelka produced an impressive comeback to beat the No.1 seed.
American Opelka saved four break points in the deciding set against the home favourite to record a 2-6 7-5 6-4 victory in one hour and 55 minutes.
Opelka will line up against Borna Coric in the quarter-finals after last year’s runner-up won 6-3 7-5 against Russian wildcard Roman Safiullin.
Denis Shapovalov also progressed to the next stage with a straightforward 6-1 6-4 victory over Belarusian qualifier Ilya Ivashka.
He will face Stan Wawrinka for a place in the last four. In the late match, sixth seed Milos Raonic beat Alexander Bublik 6-3 6-2.
Britain’s Cameron Norrie will face Andrey Rublev for a place in the semi-final.
After Norrie claimed his 50th ATP Tour victory by defeating Miomir Kecmanovic in three sets on Wednesday, Rublev advanced to the last-eight by defeating Ugo Humbert.
The No.3 seed saw off the Frenchman in two hours and 13 minutes following a 4-6 6-4 7-5 victory.