DENIS Shapovalov may only be 19, but the teenager showed maturity beyond his years in a heartwarming display of sportsmanship at the US Open.

No. 28 seed Shapovalov moved into the second round when his good friend and opponent, Felix Auger-Aliassime, was forced to retire; feeling faint, and with a racing heart rate.

Shapovalov was leading 7-5, 5-7, 4-1 when Auger-Aliassime, who had already been visited by a doctor during a changeover in the third set, called quits on the clash.

Auger-Aliassime, 18, was visibly upset on the court; breaking down in tears. Shapovalov comforted his friend, before speaking to TSN post-match.

“It’s honestly really tough, with the way it ended,” Shapovalov said.

“Obviously I hope that Felix recovers quick, and I told him at the net: ‘We’re going to play a lot more times, we’re going to be back here playing in the finals one day.’

”So I told him to keep his head up, he’s had such a great run, and it was a great match today.”

Their combined age made this the youngest U.S. Open men’s match since 2006, when Novak Djokovic, 19, beat Donald Young, 17.