Fan favourite Diaz (26-10, 2 no contests), older brother of Nate, had not competed in six years ahead of his rematch with Lawler (29-15), which took place 17 years after the old rivals’ first meeting.
Diaz, 38, looked slow and fragile in the early exchanges of the middleweight bout, which had originally been scheduled as a welterweight contest.
While he was able to show that his signature durability has not waned entirely, and while his striking speed did improve across the best part of 15 minutes, ultimately the Californian’s body and lack of motivation betrayed him at Las Vegas’ T-Mobile Arena.
The end came 44 seconds into the third round of what was optimistically scheduled as just the second ever UFC fight to be set for five rounds despite not being a title bout or main event.
With former welterweight champion Lawler having found success in sneaking uppercuts and hooks under and around Diaz’s guard, it was indeed a right hook that dropped Diaz midway through the fight.
Lawler, 39, beckoned Diaz back to his feet, but Diaz declined to keep fighting after referee Jason Herzog asked the downed icon whether he wished to continue.
In the main event, Alexander Volkanovski (23-1) retained his featherweight title in an instant classic with Brian Ortega (15-2, 1 NC), outpointing the jiu-jitsu specialist over five rounds after surviving numerous submission scares.
In the co-main event, Valentina Shevchenko (22-3) made a sixth successful defence of her flyweight title by stopping Lauren Murphy (15-5) with ground and pound in the fourth round.