David Goffin saved five set points and negotiated an underarm serve before defeating Alexander Bublik 6-3 7-6 (9-7) at the Open Sud de France.
World number 10 Goffin has started the season in impressive form and remains on course for a first ATP Tour title since Tokyo in 2017.
The second seed bested Bublik's varied strokeplay over the course of one hour and 47 minutes, with the 22-year-old even serving underarm in a bid to deceive Goffin as a gripping second-set tie break slipped away.
Goffin will face Pierre-Hugues Herbert in the quarterfinals after the home favourite claimed an impressive 7-6 (7-2) 7-5 triumph against Felix Auger-Aliassime.
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Herbert was a finalist in Montpellier last year, while countryman Richard Gasquet remained in contention for his fourth win at the event by beating Feliciano Lopez 6-7 (1-7) 6-4 6-2.
Vasek Pospisil, a winner in the all-Canadian clash with Denis Shapovalov on Wednesday, is up next for Gasquet, who retained his place in a draw stacked with French hopes.
Gael Monfils came from a set down to beat compatriot Adrian Mannarino 4-6 6-1 6-4, joining Gregoire Barrere – a shock winner over Grigor Dimitrov a day ago - in the last eight.
Filip Krajinovic will be Barrere's next opponent after demolishing qualifier Mikael Ymer 6-1 6-1, with Norbert Gombos also seeing off Emil Ruusuvuori in straight sets.
Elsewhere, seeds Ricardas Berankis, Kwon Soon-woo, Yuichi Sugita, James Duckworth and Egor Gerasimov emerged unscathed to reach the quarter-finals.