Anthony Joshua halted Otto Wallin with a fifth-round technical knockout, while Joseph Parker surprised Deontay Wilder with a unanimous decision in a heavyweight doubleheader at Kingdom Arena on Saturday night.
The doubleheader was expected to set up a March bout between Wilder and Joshua.
Instead, it appears Parker is in a position to step up in March, with the winner of that fight hoping to get a shot at the undisputed championship, which will be decided on Feb. 17 when Tyson Fury and Oleksandr Usyk meet in Saudi Arabia.
The heavyweight division hasn't been unified this century.
The 31-year-old Parker, a significant underdog according to FanDuel Sportsbook, looked like the better fighter throughout, while the 38-year-old Wilder looked his age in a matchup of former heavyweight champions.
Parker (34-3-0) dominated from the start, landing powerful punches with his right hand while keeping Wilder on his heels with a smart and methodical approach.
"It was a dangerous fight, a tough fight. We trained very hard for this," Parker said.
"We had great momentum coming into this fight. The strategy was to stay calm, stay relaxed, stay focused ... every minute of every round. This is a great finish to the year."
There was only one round in which Wilder got the better of Parker.
"My timing was off a little bit," Wilder said.
"He did a great job of avoiding a lot of my punches. I did feel like I had the upper hand, but things happen. We move on to the next step."
In the main event, Wallin's corner called for the stoppage at the end of the fifth round.
Joshua, a strong favorite, needed more than just a victory to convince skeptics that his best days weren't behind him. The British boxer earned some style points against the 33-year-old Wallin, who is from Sweden.
Joshua (27-3-0) hadn't looked the same since holding the WBA, IBF, and WBO titles. But the 34-year-old delivered a throwback performance, jabbing and moving forward with confidence while backing down Wallin (26-2-0).
A strong right-left combination in the fifth round eventually led to the stoppage.
"Just another fight. I respect Otto," Joshua said.
"Not so much a throwback, just another day in the office. I'm just a gifted fighter that has a special gift and I use it to the best of my ability."
"We just want to do whatever it takes to be victorious. All I want to be is just be victorious for as long as I can. I'm searching for greatness."
Earlier, Dmitrii Bivol defeated Lyndon Arthur in a unanimous decision that saw all three judges score it a 12-round sweep for the IBO light heavyweight and WBA super light heavyweight belts.
The early card also included five knockouts.
Daniel Dubois (20-2-0) registered a 10th-round technical knockout of Jarrell Miller (26-1-1) with 8 seconds left in the final round.
Agit Kabayel (24-0-0) scored a fourth-round TKO of Arslanbek Makhmudov (18-1-0) in a scheduled 10-round heavyweight bout.
Jai Opetaia scored a first-round knockout of Ellis Zorro in a cruiserweight fight. After changing levels throughout the round, Opetaia (24-0-0) unleashed a vicious left hook that dropped Zorro (17-1-0).
Filip Hrgovic (17-0-0) stopped Mark De Mori (41-3-2) with a first-round TKO.
Frank Sanchez (24-0-0) opened the night with a seventh-round knockout of Junior Fa (20-3-0).
