Shelton's serve-and-volley style earned him the first set, but Auger-Aliassime equalized by winning the second set in a tiebreak and then broke the American's serve to seal the match on his third match point in the deciding set.

Both competitors had lost their initial round-robin matches, with Shelton defeated by Alexander Zverev and Auger-Aliassime by the reigning champion Jannik Sinner. This hard-earned victory gives the Canadian a genuine opportunity to advance to the semi-finals.

Auger-Aliassime required medical attention during his loss to Sinner, but he dismissed those concerns, even as Shelton surged to a 4-1 lead in the first set.

The American lost his composure when he failed to serve out the set, throwing his racket in frustration after Auger-Aliassime narrowed the gap to 5-4, yet Shelton managed to break the Canadian once more.

"He was playing much better than me at the start," Auger-Aliassime admitted.

"It's rare that I get broken twice in the first set indoors."

Shelton created the only break point in the second set, but Auger-Aliassime immediately broke in the tiebreak to take a 3-0 lead.

Shelton’s struggles in the tiebreak

The American injured his knee trying to change direction quickly, limping through the remainder of the tiebreak, yet he saved three set points before a double fault ended his brave effort. Shelton did not require medical treatment.

The Canadian had break points at 2-1 in the final set but had to wait until the last game when Shelton gifted match points, which Auger-Aliassime gladly accepted.

"It was a strange start, but as the match progressed, I found ways to get my returns in play," the Canadian explained.

"Once the rallies started, I felt more confident about winning."

Later on Wednesday, Sinner will face two-time champion Zverev in the other Bjorn Borg Group match, where the Italian can clinch a semi-final berth with a win, while Zverev must win in straight sets to guarantee his place in the last four.