Grant, who was a slight underdog, needed just 2:07 to close out the bout.
Maynard came out throwing fire, but it was Grant who caught him with the fight's first haymaker, a straight right that put Maynard down. Grant smelled blood and swarmed with a barrage. He hurt Maynard further with a knee against the fence, crumpled him with another right and then mercifully, the end came following a few ground strikes.
"I worked on that exact combination," he told the MGM Grand Garden Arena crowd afterward. "It was just beautiful. I have nothing but respect for Gray."
Grant's rise has been swift and decisive. At welterweight, he was essentially a journeyman, just hanging on to his job. But since moving to 155, he's been a battering ram, a perfect 5-0 with three finishes.
As a reward, he gets Henderson, as promised before the fight.
"I know what Dana said. I want to fight Benson Henderson for the title," he said. "Nothing but respect but I want to be the champ."
Grant is now 21-5. Maynard suffered only his second career defeat, and is now 11-2-1 with 1 no contest.