Masvidal (34-13) ran directly at Askren (19-1) to open the bout and landed a flying knee as Askren ducked his head. Askren immediately stiffened up before dropping to the canvas. Masvidal landed a couple more strikes on the ground, but Askren appeared to already be out cold.
"He's so predictable, man. He's a scrub," Masvidal said when asked why he decided to try a flying knee to start. "A part of me wanted to just throw it out there so he knew, if you do shoot [for a takedown], like an idiot, like you only know how to, your head's going to get clipped, and then I would put the brakes on him and beat him up for 14 minutes and 30 seconds and execute him. Or, you know, he took the bait. ... He walked right into it."
Askren remained on the canvas for several minutes and appeared still dazed when he finally stood up. He was led out of the Octagon with assistance from his team and was transported to a local hospital.
Askren told ESPN's Ariel Helwani late Saturday night that he was discharged and was attending his after party.
Askren also took to Twitter afterward to sum up his knockout loss.
Well that sucked— Ben Askren (@Benaskren) July 7, 2019
Masvidal and Askren had a contentious buildup to Saturday's fight, throwing out their share of taunts and insults at each other during prefight promotional events.
The taunting continued in the immediate aftermath of Saturday's fight, when Masvidal got down on all fours next to an unconscious Askren and began slapping the ground.
White's reaction to Masvidal's flying knee: 'Wow'
Dana White calls Jorge Masvidal's flying knee on Ben Askren "one of the most vicious knockouts" he's ever seen in his life. For more UFC, sign up here for ESPN+ http://plus.espn.com/ufc.
Masvidal said he had no remorse for the strikes that came after Askren was knocked unconscious. When a reporter suggested some people felt the punches were unnecessary, Masvidal shot back, "They were super-necessary."
"The referee hadn't pulled me off, and my job is to hit somebody until the referee pulls me off," he said. "So to those people, I would say maybe don't watch MMA, and go back to soccer."
Duane Ludwig held the previous UFC record for fastest knockout (six seconds) against Jonathan Goulet in 2006.