On Saturday, the Australian defeated Romero again to retain his middleweight title -- this time with an injured hand.
Whittaker (20-4) edged Romero in a close split decision at UFC 225 at the United Center. Two judges scored the contest 48-47 for Whittaker, while a third had it 48-47 for Romero.
The two met previously at UFC 213 last July. Whittaker won via unanimous decision despite tearing the MCL in his left knee in the opening round. He had to overcome an injury again Saturday, as he hurt his right hand early in the fight.
"Yoel must be bad luck, mate, because the first round I busted my hand. I cannot feel it up to here," Whittaker said, pointing at his right hand. "It was absolutely brutal."
Technically, the five-round fight wasn't even for Whittaker's title, because Romero missed weight by two-tenths of a pound during Friday's official weigh-in. Had Romero (13-3) won the bout, it would have thrown the 185-pound division into a weird state, as the official champion would have been coming off a loss.
Romero, 41, did his best to do just that. After a conservative start, Romero dropped Whittaker with a right hand early in the third round. The shot seemingly came out of nowhere, after Whittaker had his way in the first two rounds and even closed Romero's right eye with punches.
Whittaker survived the third, despite an onslaught of offense from Romero. He even responded at times, with standing elbow strikes that momentarily backed Romero off.
Romero dropped Whittaker a second time with a left hand in the fifth -- but again, Whittaker survived.
"He hits like a truck," Whittaker said. "I know he looks weak, but he packs some power. I can tell you that much. He caught me in the fourth and fifth, and I was just trying to survive.
"It could have gone either way. I hit him with a lot. I thought I controlled three of the five rounds, but he did drop me in the fourth and the fifth. So it was anybody's guess. It was tight."
Romero, a former Olympic silver medalist in wrestling for Cuba, did not make a huge fuss over the score, but he did say he felt he won.
"It is my humble opinion I did not lose tonight," Romero said.
UFC president Dana White has suggested Romero needs to move up in weight, to the 205-pound division. He has missed weight for his past two bouts.
Whittaker has now won nine fights in a row.