No less than a classic was expected from lightweights Eddie Alvarez and Justin Gaethje on Saturday in their bout on the main card of UFC 218 at Little Caesars Arena in Detroit, and a classic they delivered.

Alvarez handed the previously undefeated Gaethje the first loss of his career by stopping him with a brutal knee at 3:59 of the first round. Alvarez could barely stand from all of the punishment his lead leg took from Gaethje kicks. He had a baseball-sized welt on the right side of his jaw, yet still managed to come out on top.

Alvarez finished it with a perfectly placed knee to the jaw in the center of the ring. Gaethje slumped face first to the mat, and Alvarez raised his arms skyward in triumph in a bout that won’t soon be forgotten. Referee Herb Dean stopped it at 3:59 of the third.

Alvarez, who was scoring well throughout the fight with his jab and body shots, admitted afterward that he might not have been able to make it all the way had the fight been a five-rounder instead of a three-rounder.

“It was starting to bug me,” Alvarez said of his left leg. “If this was a five-rounder, I would have needed to finish that in the third. Four and five would have been tough for me.”

Gaethje came out early and attacked Alvarez’s left leg with his kicks and was having immediate success. Gaethje’s nickname is “The Highlight” and he’s one of the most exciting fighters ever in the UFC. He attacks constantly and rarely takes a backward step.

And he took few on Saturday despite great work for Alvarez coming back at him. Alvarez was relaxed and was willing to stand in the pocket and trade. He had better striking defense than Gaethje and was able to wear Gaethje down with the strikes.

Alvarez landed 155 of 356 significant strikes he threw, and seemed to hurt Gaethje several times.

But Gaethje, who at times seems immune to punishment, kept attacking. He not only beat up Alvarez’s leg but began to swell Alvarez’s jaw, possibly with an elbow. The swelling just created another target for Gaethje, but Alvarez, the former lightweight champion, fought his way through it.

He landed the knee in the middle and sent Gaethje down. Gaethje tried to get up but his legs weren’t under him and Dean wisely stopped it.