Garbrandt, who went 32-1 as an amateur boxer, floored Brimage (7-4) with a left and a right in the third-latest stoppage of a three-round UFC bantamweight fight.
The main event at the MGM Grand Garden Arena featured the light-heavyweight title grudge match between champion Jon (Bones) Jones and Daniel (DC) Cormier.
Garbrandt (6-0) becomes the ninth fighter from the Team Alpha Male camp in Sacramento to earn a UFC win. The gym is home to bantamweight champion T.J. Dillashaw and former WEC title-holder Urijah (The California Kid) Faber.
The 23-year-old Garbrandt, a slight underdog, absorbed two kicks to the groin in the first round. But he rallied to wobble Brimage as the first round ended, saying later he thought he broke his right hand in the round.
The second started with both fighters throwing plenty of punches in a back-and-forth round that saw Garbrandt drops his hands and egg Brimage on. "Get your hands up," yelled Garbrandt's corner.
The third was more of the same as the two 135-pounders chased each other around the cage with bad intentions. Brimage pushed the pace and paid for it as Garbrandt tagged him and eventually put him away.
Four of Garbrandt's previous five fights ended in the first round and he has yet to go the distance, although he came close Saturday.
Unbeaten Paul (The Irish Dragon) Felder closed out the undercard in spectacular fashion by knocking out veteran lightweight Danny (Last Call) Castillo, another Team Alpha Male fighter, with a spinning back fist at 2:09 of the second round.
As Castillo (17-8) launched a kick, Felder (10-0) turned away and then kept revolving to throw the spinning back fist. Castillo fell backwards and eventually had to helped onto his stool.
Felder, from Philadelphia, won a split decision over Canadian Jason Saggo last time out in Halifax. He was slated to fight later this month in Boston but stepped up to face Felder after Rustam Khabilov withdrew through injury.
He looked razor-sharp in handling Castillo, whose UFC record fell to 7-5
Lightweight Evan Dunham (15-6) lived up to his 6-1 odds by punishing Brazil's Rodrigo Damm with strikes en route to a unanimous 30-27 decision. Damm (12-9) slapped himself several times in the dying moments of the fight, as if to say Dunham's punches were not hurting him. But the blood on his face told a different story.
"At the end of the third round I knew I was behind on the judges' scorecards so I tried to taunt Evan into an exchange," Damm explained later.
Both men badly needed a win. Dunham had lost three straight while Damm, a former world champion in Brazilian jiu-jitsu, had lost his last two.
Former LSU fullback Shawn (The Savage) Jordan, a six-foot load at 261 pounds, knocked out UFC newcomer Jared (Tha Killa Gorilla) Cannonier at 2:57 of the first round and then defied gravity by doing a backflip in the cage. Jordan felled Cannonier (7-1) with a right to the back of the head and then finished him off with strikes on the ground.
"I would really like to fight someone who's ranked higher than me next," Jordan said. "It's time for me to start climbing the ladder."
The 30-year-old Cannonier, whose day job is repairing air traffic control equipment for the Federal Aviation Administration in Anchorage, took two months off work to prepare for the fight, raising more than $6,000 through gofundme.com to pay for his Arizona training camp.
At 235 pounds, Cannonier was giving up 26 pounds. He did well until Jordan (17-6) caught him.
Russian welterweight Omari Akhmedov (14-2) spoiled Mat Nilsson's debut at welterweight, taking a unanimous 29-28 decision over the Danish-based Swede. Akhmedov slowed as the fight progressed and Nilsson (11-4-1), a former world champion grappler, was trying to lock up a D'arce choke when the fight ended.
Bantamweight Marion (The Belizean Bruiser) Reneau, a hard-nosed high school teacher making her UFC debut at the age of 37, used her superior striking skills to bloody up Alexis (Sneaky Zebra) Dufresne (5-2) en route to a lopsided unanimous (30-26, 30-26, 30-25) decision.
"Who's next?" Reneau (5-1) said after the fight.
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