Roger Federer suffers shock second-round defeat in Halle
"It's amazing, for sure I didn't expect this," Auger Aliassime told Eurosport after beating one of his heroes at the first attempt on the ATP tour.
"I wanted to win, but Roger Federer is my idol and it was a huge honour to play him."
Federer is exactly 19 years older than Auger Aliassime as the pair share the same birthday on August 8, while the Swiss ace turns 40 this year.
"I always thought he would be gone by the time I joined the tour," admitted the Canadian, who turned professional in 2017.
"I was a little nervous when I realised I could win, but I was playing really well, almost perfect tennis."
Federer had pulled out of the fourth round of the French Open last week to give himself extra rest after two operations on his right knee in 2020 and a year of rehab.
Halle is his traditional grass court warm-up event before playing at Wimbledon and he won the tournament played near Bielefeld for the tenth time in 2019.
However, despite losing the first set, Auger Aliassime, ranked 21 in the world, showed no signs of being intimidated by Federer, who has won 20 Grand Slams.
The Canadian blasted down 13 aces and earned 15 break points, of which he managed to covert just three.
Federer, who had said he needs ten games to prepare for Wimbledon, won the first set with ease, but struggled from there on.
He soon started to labour in the second set as Auger Aliassime converted his fourth break point to go 4-2 up, then served out to level the match at one set all.
It was one-way traffic in the deciding set as Auger Aliassime broke Federer to take a commanding 3-0 lead and eventually converted the first of his three match points.
In the quarter-finals, the Canadian will play either German Jan-Lennard Struff, who knocked out top seed Daniil Medvedev in the first round, or American qualifier Marcos Giron.
Auger Aliassime is hoping to win the first ATP title of his career in Halle after losing all of his last eight finals, including last week's grass court tournament in Stuttgart.