Romero is best known for his explosive finishes and he delivered once again after blasting Rockhold with an overhand left that sent him tumbling to the canvas in the third round.
Romero followed up with an absolutely crushing left uppercut that put Rockhold out as the Cuban-born middleweight earned his sixth knockout in the third round since joining the UFC roster back in 2013.
While Romero was actually the No. 1-ranked middleweight going into the fight, he was a slight underdog according to fantasy players, with 44 percent picking him to win. The overwhelming majority of those who did select Romero correctly predicted that he would win by knockout, with 87 percent calling the outcome in the fight.
In the co-main event, Curtis Blaydes picked up one of the biggest upsets all night as he earned a hard fought unanimous decision over Mark Hunt in a heavyweight showdown. Blaydes survived an early scare from Hunt in the first round before using his wrestling to control the heavy-handed New Zealand native for the majority of the remaining 15 minutes. Only 31 percent of fantasy players picked Blaydes going into the event, but he'll probably get a few more picks on his side the next time he competes after his performance on Saturday night.
Australia's own Tai Tuivasa put on another stunning performance as he knocked out Cyril Asker in the first round of their fight on the UFC 221 main card. Tuivasa was a heavy favorite, with 81 percent of fantasy players picking him to win and another 78 percent predicting that he would win by knockout.
Jake Matthews also picked up a unanimous decision win over Li Jingliang in a back and forth battle at 170 pounds. Matthews was a slight favorite, with 59 percent of fantasy players picking him as he moves to 2-0 since returning to welterweight.
In the kickoff bout on the Pay-Per-View main card, Tyson Pedro made short work of Saparbeg Safarov with a first-round kimura to win by submission after an overwhelming 85 percent of fantasy players picked him to win on Saturday night.
In the featured prelim, Dong Hyun Kim got a razor close split decision victory over local favorite Damien Brown, with 61 percent of fantasy players predicting that he would get the job done at UFC 221.
Highly touted prospect Israel Adesanya made his debut on Saturday night as he dished out a second-round TKO to finish Rob Wilkinson in a middleweight battle. Adesanya could be a future star in the UFC and he showed why as he picked Wilkinson apart on the feet before getting the finish, with 67 percent of fantasy players correctly predicting his victory. Adesanya also earned an extra 40 points because it was his Octagon debut.
Alexander Volkanovski made quite a statement in his matchup with previously undefeated featherweight Jeremy Kennedy as he bashed his way to a TKO win with a series of hard punches and elbows on the ground. Volkanovski was a very solid favorite going into the night, with 73 percent of fantasy players picking him to win as he continues to move closer and closer to the top 15 at 145 pounds.
Despite having a higher ranking going into the fight, Jussier Formiga was actually a big underdog in his matchup against Ben Nguyen, but the Brazilian showed why he's been one of the bset flyweights in the world for some time now as he flattened his opponent with a spinning backfist before finishing the fight with a rear naked choke on the ground. Just 38 percent of fantasy players picked Formiga, and he also earned an extra 120 point bonus because it was a tight matchup on paper.
Ross Pearson got back on track with a unanimous decision win over Mizuto Hirota on the early prelims, with 77 percent of fantasy players picking the former Ultimate Fighter winner to get the job done.
Meanwhile, Jose Quinonez pulled off an upset with his win over Teruto Ishihara after just 37 percent of fantasy players picked him, while Luke Jumeau came away as a big favorite, with 72 percent selecting him as he was victorious by unanimous decision over Daichi Abe in the kickoff fight of the night
All told, eight favorites were victorious at UFC 221, with only four upsets according to the selections made by fantasy players ahead of the card.