"I didn't expect that," world number 71 Lehecka, who made his breakthrough last year by reaching the Rotterdam semi-finals as a qualifier, told reporters.
Hopefully we'll go one more step, step after step.
"To be in those moments and be cool under pressure, play well the right points, serve well to close the match, it's a good sign of a good player," Auger-Aliassime said.
"Yeah, I'm sure for those reasons he'll be a good player in the future."
Up next for Lehecka is a potential meeting with third seed Stefanos Tsitsipas, his conqueror in the Rotterdam semi-finals, if the Greek gets past Jannik Sinner.