Known as an aggressive striker, Belfort (23-10) instead paced himself as the engaged in the early going and showed restraint by not overcommitting against the larger Rockhold (10-2).
But when the opportunity presented itself, Belfort delivered an incredible spinning heel kick that landed flush on Rockhold's chin and sent him toppling to the floor. Belfort pounced with a flurry of punches on the ground, and referee Leon Roberts called off the fight at the 2:32 mark of the first round.
Belfort, who has been heavily criticized in some circles for his commission-approved use of testosterone-replacement therapy improves to 4-1 in his past five fights and may have moved himself back into title contention at 185 pounds. The Brazilian is now 10-2 in the past six years with both losses coming to the men largely considered the world's two best fighters in Jon Jones and Anderson Silva.
Still, Belfort said he'll wait for the UFC to issue his next assignment rather than ask for a specific opportunity.
"I'm here to fight," Belfort said after the win. "I don't pick fights. I accept fights."
Belfort was awarded a US$50,000 bonus cheque as the evening's "Knockout of the Night."
In the night's co-feature, former Strikeforce middleweight champion Ronaldo "Jacare" Souza (18-3) flashed his impressive jiu-jitsu skills in a first-round stoppage win over Chris Camozzi (19-6).
Souza wasted little time getting the fight to the floor in the opening round, and while Camozzi showed capable defence for several minutes, "Jacare" was too much on the floor. The multiple time jiu-jitsu world champion quickly latched on an arm-triangle choke and squeezed tight, putting Camozzi to sleep in mere seconds. The official time came at the 3:37 mark of the first frame.
With an impressive win in his UFC debut, Souza immediately establishes himself as a contender in the promotion's 185-pound division.
"Everyone was asking if I was going to get the jitters, but I didn't because of the crowd — the crowd has been fantastic," Souza said. "We were grappling, and I was waiting for him to give me the opportunity. I saw his neck, and I just went for it."
Souza also pocketed an extra $50,000 as the evening's "Submission of the Night" winner.
In a key lightweight contest, Brazilian slugger Rafael dos Anjos (19-6) earned a controversial split-decision win over American Evan Dunham (14-4).
The pair traded shots on the feet throughout the 15-minute affair. It was dos Anjos who appeared to hold the power advantage, but a gritty Dunham consistently walked forward and linked together combinations. A pair of late takedowns in the opening to rounds appeared to earn Dunham the frames, but judges disagreed and awarded a unanimous-decision win with scores of 30-27, 29-28 and 29-28.
UFC president Dana White, who was not in attendance for the event, immediately took to Twitter to protest the decision.
"Dunham got ROBBED!!!!" White wrote.
In the night's first main-card contest middleweight Rafael Natal (16-4-1) earned a unanimous decision over local hero Joao Zeferino (13-5).
Zeferino, who earned his way on to the card as an injury replacement with less than three-weeks' notice, looked sharp in the opening round but visibly tired as the contest wore on. Natal, while cautious, controlled the pace and positioning over the final 10 minutes en route to the clear-cut decision win.
"I knew that being called on in such short notice, he wouldn't have enough time to get in shape," Natal said after the win. "I thought that although I lost the first round, I was going to get the second and third, and that's what happened."
UFC on FX 8 drew a reported 7,642 fans, according to UFC exec Marshall Zelaznik.