Auckland - World No 13 Denis Shapovalov crashed out of the ATP Auckland Classic on Thursday, beaten in straight sets by French qualifier Ugo Humbert.
There was only one break in each set of the evenly contested clash with Humbert winning 7-5, 6-4, clinching the victory with the Canadian's sixth double fault.
"I'm really, really, happy, it's one of the biggest wins of my career," the 57th-ranked Humbert said as he advanced to a semi-final showdown big-serving American John Isner.
"I tried to play each ball, I tried to stay focused and my plans were working."
Isner survived on his thunderous serve with an impressive 25 aces to overcome Kyle Edmund in the opening quarter-final.
While Edmund had the better of the fourth seed for much of the match, Isner served his way out of trouble when it mattered and the Briton was unable to convert any of his nine break points.
Both sets went to a tiebreak before the American won 7-6 (7/5), 7-6 (7/5) and expressed relief at making the final four.
"I know I was a bit fortunate to win today, that's how tennis goes, but I'm happy I'm in the semi-finals," said the two-time Auckland champion who holds the world record for the most aces in a match with 113 against Frenchman Nicolas Mahut at Wimbledon two years ago.
"That match point, I played it very aggressively and very well. Winning a match like this can give me a lot of confidence going forward for the rest of this tournament, the Australian Open and for the rest of the year."
The remaining quarter-finals are between fifth-seed Frenchman Benoit Paire and Australian John Millman, while sixth-seed Hubert Hurkacz of Poland will play Spain's Feliciano Lopez.