Bruno Fernandes scored an extra-time penalty to secure United’s place in the semi-finals.
But Martial was the star of the show, despite his finishing not being up to scratch, and Hargreaves heaped praise on the 23-goal striker.
He told BT Sport: “Everyone’s got an opinion on Martial. He’s a Ferrari. He just looked like a £100million player.”
Paul Scholes added: “He’s turning into a No 9 more and more every game I watch.
“He’s normally a brilliant finisher but tonight the finishing wasn’t quite there.”
Another former United hero, Robin van Persie, was also in awe of Martial’s performance, claiming his teamwork and vision sets him apart from others.
The Dutchman added: “Martial always have an eye for his team-mates and that’s what sets him apart from the others.
“That’s why I think he’s a world class player.”