Andrey Rublev's hopes of retaining the Kremlin Cup on home soil in Moscow are over after he suffered a surprise defeat to Adrian Mannarino.
Mannarino ultimately came out on top 5-7 7-6 (7-4) 6-3 but he had to do it the hard way, coming back from match point down to set up a meeting with Ricardas Berankis, who lost only tree games in a 6-2 6-1 win over Federico Coria.
Rublev was never cruising, however, as Mannarino only just fell short in the first set and then took the second to a tiebreak, which he eventually won to turn the tide.
The 33-year-old, who lost to Rublev in the final two years ago, took things up a notch in the decider and did not face a single break point as he got the job done despite the home support.
"The crowd was cheering for Andrey but that is normal," he said after reaching the quarter-finals. "I was happy to play with such a nice atmosphere.
"We have been playing for a long time without fans, so it is nice to enjoy a stadium with crowds now."
Second-seed Aslan Karatsev is now the favourite in Moscow, and the Russian had few issues in a 6-4 6-3 defeat of Egor Gerasimov.
Karatsev will face Gilles Simon next following his 6-3 6-2 win over Mackenzie McDonald, while Pedro Martinez won 6-3 6-4 over Filip Krajinovic to book his passage.
At the European Open in Antwerp, Andy Murray's hopes of winning a first ATP Tour title in two years were ended by number two seed Diego Schwartzman.
The Argentinian trailed 4-1 in the first set but fought back to win 6-4 7-6 (8-6) in his first ever match against the Scot, whose last tour triumph was in Antwerp.
In his on-court interview, Schwartzman said: "It was a pleasure to play against Andy. We had not played before and he is coming back and every week he is playing better and moving better.
"I have a lot of respect because when I grew up playing tennis, I was watching Roger [Federer], Rafa [Nadal], Andy and Novak [Djokovic] and right now playing against him is a pleasure for me."
Seventh seed Lloyd Harris is also into the quarter-finals after a straightforward 6-2 6-3 victory over Jan-Lennard Struff in just 72 minutes, Marton Fucsovics came through 6-7 (5-7) 6-3 6-1 against Roberto Bautista Agut and Brandon Nakashima edged past Henri Laaksonen 7-6 (7-5) 6-7 (5-7) 6-3 to earn the right to face Schwartzman.