The top seed is out of the National Bank Open presented by Rogers men's tournament after just one match.
Germany's Alexander Zverev lost 6-7 (3), 6-2, 6-4 to world No. 69 Tallon Griekspoor of the Netherlands in a second-round match on Wednesday in Montreal.
Like all seeded players, the 2026 French Open champ got a bye in the first round.
Zverev won the NBO in 2017.
The tournament's second seed, Canada's Felix Auger-Aliassime, didn't even make it onto the court. He withdrew prior to his scheduled match Wednesday with a back injury.
Zverev, who won his first career Grand Slam earlier this season at the French Open, fired 10 aces to four double faults, while Griekspoor had eight and two, respectively.
The German won just 48 per cent of points on second serve and had just one break-point opportunity, though he did manage to convert.
Overall, Griekspoor won 96 points to 78 for Zverev, including a four-for-nine conversion rate on break-point opportunities.
Zverev was among a host of seeded players to exit on Wednesday at the National Bank Open, also including No. 2 Auger-Aliassime, No. 7 Taylor Fritz, No. 14 Valentin Vacherot, No. 16 Francisco Cerundulo, No. 25 Alejandro Tabilo, No. 26 Tomas Etcheverry, No. 29 Ignacio Buse and No. 32 Raphael Collignon.
