Souza (27-6) finished Weidman (14-4) via TKO at 2:46 of the third round in their middleweight contest, the co-main event of UFC 230 inside Madison Square Garden.
It was a very close fight up until the finish. Souza knocked Weidman down with a heavy right hand, but referee Dan Miragliotta did not immediately step in. Souza threw a couple of more punches and protested to Miragliotta as he did. Weidman weakly grabbed for Souza's leg, and Miragliotta then waved off the fight.
"I love Chris," Souza said. "He's a great guy. He's a hero and a legend in the sport. He's a great guy. I know he's here, in his hometown. I feel bad for him. I love this guy. He is the best in the world."
It's the second time Weidman has been viciously knocked out inside Madison Square Garden. He suffered a flying-knee knockout loss to Yoel Romero two years ago at UFC 205. That finish also occurred in the third round.
A former UFC champion, Weidman outstruck Souza on the feet early and bloodied his nose with jabs. The entire bout took place on the feet, despite Weidman's collegiate wrestling background and Souza's decorated jiu-jitsu career.
Souza, of Manaus, Brazil, responded in the second and third rounds. He repeatedly went to the right side of Weidman's body with the left hook and followed it with overhand rights. Weidman struggled to defend the right hand, specifically, which proved to be the difference in the contest.
A former Strikeforce champion, Souza has never fought for a UFC title despite a 9-3 record in the Octagon. He missed significant time last year due to injury, but Souza is 2-1 in 2018, including finishes over Weidman and Derek Brunson.
Adesanya puts on a knockout of a performance
Adesanya negated Brunson's early attempts to get him to the floor before landing a hard knee to the chin in a scramble. Brunson backed off and tried to regain his wits, but Adesanya smelled blood. He followed up with more knees, dropped him with a right hand and eventually finished him with punches against the fence.
The finish came at the 4:51 mark of the opening round.
"They say I ain't got no wrestling. This was like a walk in the [park]," Adesanya said. "No, this was like a walk in the garden. Madison, baby."
Adesanya, who trains out of New Zealand, has set the UFC's middleweight division on fire in 2018. Saturday's victory was his fourth victory this year. He's defeated Rob Wilkinson, Marvin Vettori, Brad Tavares and Brunson.
Cannonier stuns Branch in middleweight upset
Former light heavyweight Jared Cannonier (11-4) made the most of a short-notice opportunity, finishing David Branch (22-5) via TKO at the 29-second mark of the second round in his UFC middleweight debut.
Cannonier, of Dallas, accepted the fight against Branch late last month after Branch's original opponent, Ronaldo "Jacare" Souza, was shuffled to the co-main event. Cannonier was 1-3 in his past four bouts coming in, and he hadn't won since July 2017.
He surrendered a couple of takedowns to Branch early but made him work hard for them. It appeared to have a wearing effect on Branch, as he looked tired and uncertain between rounds. The second frame was all Cannonier, as he dropped Branch with a hard right hand and followed with finishing blows on the floor.
"I know I'm one of the best in the world, and I came here to get my hand raised," Cannonier said.
It's a huge setback for Branch, who is a former WSOF champion at middleweight and light heavyweight. Branch went into UFC 230 with a major opportunity of his own against Souza. He now falls to 2-2 since signing with the UFC last year.
For Cannonier, who fights out of MMA Lab in Glendale, Arizona, it is the sixth knockout of his career.
Roberson dominates Marshman in bloody decision
All three judges scored it a one-sided beating for Roberson: 30-26, 30-26 and 30-27. Roberson landed heavy left hands throughout the 185-pound contest, badly bloodying Marshman's nose in the process. Marshman proved to be extremely durable, but he never posed a threat to the 28-year-old Roberson.
A former professional kickboxer, Roberson showcased his wrestling as well. He took Marshman down in the second and third rounds, and worked out of side control.
The only downside for Roberson was it appeared he suffered a leg injury in the second round. Roberson limped occasionally, but it did not affect his performance. He bounced back from a submission loss to Cezar Ferreira at UFC 224 in May.