In his return from a 17-month layoff due to a knee injury, Gunnar Nelson overcame a busted nose to rally past Alex Oliveira in a fight that looked like a horror movie upon its finish.

With blood flowing from his own nose, Nelson (17-3-1) achieved full mount in Round 2 and brutally sliced open Oliveira's forehand with an elbow. With the Brazilian's face covered in a sheet of crimson, Nelson slid underneath to apply the rear-naked choke for an instant tap at UFC 231 in Toronto.

Referee Jerin Valel waved off the fight at 4:17 of the second round inside Scotiabank Arena.

For complete results from UFC 231, please click here

The welterweight bout excited the crowd due to its violence but it was Iceland's Nelson, 30, who overcame a first round in which Oliveira reversed him on the ground and reined down with hard strikes.

"It ended the way I expected but the fight was a bit of a scrap," Nelson said. "I believe he hit me in the beginning to the back of the head. He caught me with a good shot and got me a little disoriented for a while. I survived in there and I was able to get on top nicely and finish the job."

After Nelson opened the fight with a hard right hand to get his opponent's attention, Oliveira landed a questionable elbow from the clinch to the back of Nelson's head. "Cowboy" was later warned by the referee for holding the cage to avoid a takedown from Nelson.

The second round began with Nelson eating a short elbow against the cage wall that bloodied and bruised his nose. But Oliveira's attempt to force a takedown finished with him on his back and Nelson in full mount.

To his credit, Nelson never panicked, even as the referee warned him for a lack of activity. He picked his spots with short elbows and forearms before busting open Oliveira and forcing an end to the fight.

"I knew he would be covering up really well after that shot and I thought that I might slide in for the neck," Nelson said. "The blood makes things slippery, as well."

Oliveira (19-6-1, 2 NC) fell to 5-2 over his last seven bouts with the loss.