Britain's Molly McCann submitted Diana Belbita in the first round in a dominant performance on her strawweight debut at the UFC Apex in Las Vegas.
McCann, 33, finished the Romanian with an armbar with one second remaining in the round.
It was a return to form for McCann, who says she considered retirement following defeats in her previous two fights.
"It feels amazing [to be at strawweight]," said McCann.
"I'd like to take this time to apologise to the UFC, myself and my fans for not being at the right weight and for my last two performances. But today I forgive myself."
McCann had spent the entirety of her UFC career, which has yielded seven wins from 12 bouts, at flyweight, but first-round defeats by Erin Blanchfield in November 2022 and Julija Stoliarenko seven months later caused her to question her future in the sport.
Following the advice from her coach Paul Rimmer, McCann decided to drop down to strawweight, saying she was "in the best shape of my life" heading into the fight with 27-year-old Belbita.
McCann, who was a pre-fight favourite with bookmakers, wore a composed expression as she walked out for the fight, in comparison to the intensity displayed in recent encounters.
McCann was also accompanied by the walkout song used by her friend Ryan Curtis, who was involved in a "life-changing" training accident last month.
McCann started the fight with intent, landing a pair of crushing overhand rights before controlling the early stages by landing shots and quickly moving out of Belbita's range.
As the round wore on, McCann's confidence grew as she rotated through her arsenal, hitting a spinning back kick and trademark spinning back elbow.
But it was in the grappling exchanges where the fight would be decided as McCann took Belbita down, transitioned to full mount and delivered a series of elbows.
With seconds remaining in the round, McCann then locked in an armbar and secured the win.
It was a poetic finish for McCann, whose past two UFC defeats had also come by armbar, and she collapsed to the canvas as she celebrated the moment.
The victory was also her second over Belbita, whom she beat in a 2019 by unanimous decision.
"Say less, do more. The plan was to be a world champion at 125lb but it didn't work out," said McCann.
"When the plan doesn't work, you don't change the goal; you change the plan. My coach promised me this would happen and I've listened.
"Take every day as it comes. I'm going to go and spend time with my family. And my gym, I've been putting some work in - I'm going to have a beer and see you soon."