Gaethje, a modern-day barbarian who is nearly impervious to pain, seemed unfazed by a cut above his left eye in Round 1 and continued to chip away at Poirier's right leg with a steady stream of damaging kicks. And the fight delivered in spades, going back and forth before ending with Poirier hurting Gaethje and attacking him to a stoppage 33 seconds into round four.
"I've got about five fights in me".
Will he get a title shot from this win? I've shown resilience and fortitude and I've done it over and over again to put myself back in the position I'm in, and I'm hitting my stride as a father, a fighter, a husband and a person.
The end came when Poirier landed a left hand that stunned Gaethje.
He's a true warrior in every sense of the word and if we're being honest, a genuine crazy-man in the octagon but with time well and truly ticking on his career, enjoy fighters like Justin Gaethje while you can.
Gaethje, 29, who has firmly established a reputation in three UFC fights for providing entertainment, also suffered his second straight defeat via violent knockout.
"I've paid my dues", Poirier said. "I'm a UFC employee and I know I have to be ready when it comes".
Poirier was still ahead on all three cards and left no doubt in the fourth round, stunning Gaethje with the left hand and burying him in a flurry of punches until Dean stepped in to stop it.
Poirier added: "This guy [Gaethje] would have died in here if Herb Dean hadn't stopped it". Coming off two losses, that's hard to say, but you want to see me fight.