UFC 221 took place in Perth, Australia.
Romero, who rescued the main event by stepping in to replace the injured Robert Whittaker some weeks ago, missed championship weight on Friday to leave himself ineligible for the interim middleweight title strap.
In the co-main event of the evening American heavyweight Curtis Blaydes overcame an early scare to score the biggest victory of his MMA career as he outpointed Kiwi legend Mark "Super Samoan" Hunt after a gruelling three-round battle. We will bring you all the results starting at 3:30 PM Pacific Time. And with another night of UFC action in the rearview mirror, it's time to look forward, put on a pair of Sean Shelby and Mick Maynard's shoes, and play UFC matchmaker for UFC 221's losing fighters. Both fighters have serious knock out power and I don't expect this fight to reach the third round.
The next UFC show sees the octagon land in Austin, Texas, next weekend for UFC Fight Night, with welterweight fan favourite Donald "Cowboy" Cerrone facing Hawaiian Yancy Medeiros in the main event.
After Rockhold had gathered some of his scattered bearings, Romero tried to console him, something that made for a hard watch.
But the massive Cuban will get the opportunity to fight for the only belt that matters after knocking out Rockhold with two crushing left hands.
Another said: "Second punch wasn't a finisher, it was an assassination".
Hunt landed a huge shot to drop Blaydes early in the fight, prompting Blaydes to turn to his wrestling.
"Rockhold is a very good athlete and an unbelievable fighter", Romero said after the fight.
"Typical. Par for the course with Yoel Romero", Rockhold responded, later posting on Twitter: "Should have be doing the salsa in the sauna".
A crowd of 12,437 attended Sunday's fight.
Had he beaten Romero, Rockhold might have chose to stick around for a crack at Whittaker but after falling to his second defeat in three fights, a move 20lbs north can't be far away for the 33-year-old veteran.
Come fight night, Australia will be represented by Tai Tuivasa, Jake Matthews and Tyson Pedro, who lock horns with Cyril Asker, Li Jingling and Saparbek Safarov respectively.