Alexander Bublik of Kazakhstan downed US fourth seed Taylor Fritz 7-6 (7/5), 6-2 on Thursday to book his spot in the quarter-finals of the Paris Masters.
Lying in wait for the 13th seed in the next round will be either Russian 10th seed Karen Khachanov or sixth seed Alex de Minaur of Australia.
The maverick Bublik has been in fine form in Paris this week and came from behind in the first-set tie-break to seal the opener against the world number four Fritz.
Bublik broke the American to move 4-2 ahead in the second set, before again pouncing on Fritz's serve and sealing victory with a winning return, AFP reported.
Defeat for Fritz came a day after he secured his place at the ATP Finals following world number eight Lorenzo Musetti's second-round exit in the French capital.
Earlier, American fifth seed Ben Shelton beat Russia's Andrey Rublev 7-6 (8/6), 6-3 in the third round and will next face either Argentina's Francisco Cerundolo or former world number one Jannik Sinner in the last eight.
The 23-year-old edged a tight opening set against 12th seed Rublev after nearly an hour on court.
The big-serving Toronto Masters champion then secured the first break of the match in the seventh game of the second set to close in on victory.
Shelton engineered several match points in Rublev's next service game, before eventually converting at the third time of asking.
Canada's Felix Auger-Aliassime booked his place in the quarter-finals as he came from behind for the third time in as many matches in Paris to beat German Daniel Altmaier 3-6, 6-3, 6-2.
The ninth seed is currently one spot outside the last ATP Finals berth, which is occupied by Musetti, who lost Wednesday to fellow Italian Lorenzo Sonego.
That result coupled with an Auger-Aliassime run to the title-decider in Paris would send the 25-year-old above Musetti in the race to the eight-man season-ending showpiece in Turin.
However, before he can think too much about that, Auger-Aliassime must stop the in-form Valentin Vacherot of Monaco.
The Shanghai Masters champion continued his sensational run of form by ousting Carlos Alcaraz's British vanquisher Cameron Norrie in straight sets in the opening match on center court.
Later, four-time Grand Slam winner Sinner will seek to keep alive his hopes of reclaiming the world number one ranking when he takes on Cerundolo in the night session.
