The Brazilian had previously stated he'd wait until champion Dominick Cruz was healthy, but he had no issue rising to the occasion and taking on one of the youngest up-and-coming contenders in the promotion.
McDonald was vying to become the youngest champion in UFC history, but "Mayday" ran out of steam after about two hard-fought rounds, en route to a fourth round submission defeat at the hands of the interim bantamweight champion.
Early on, McDonald looked solid, working to mix in his power strikes to counter Barao's aggression. The Brazilian made his gameplan evident very quickly, scoring a takedown inside the opening minute, but McDonald did a good job of shutting his aggression down and working his way back to his feet.
Once there, "Mayday" looked to land that big power strike, but he had some trouble finding a home for it while in the open, but Barao gave him an opportunity when he closed the distance along the fence, allowing McDonald to score with some swift short strikes that hurt the interim champion, wobbling him along the cage and forcing the Brazilian to shoot in for a takedown to clear out the cobwebs.
Barao would survive to the second round, but his aggression disappeared at least in the beginning, handing over control of the action to McDonald and allowing the young American to handle the distance, pace and activity level of the frame.
That all changed in the final minute as Barao scored with a punching combination and then blasted McDonald with a front kick to the face to potentially win back the round and seize control of the fight once more.
McDonald's corner implored him to try to finish the fight because they didn't want the bout to go to a decision, but McDonald was running out of stream. Barao controlled the third round with a big takedown where he almost advanced to mount and then proceeded to outwork McDonald on the feet with good striking combinations capped off by a heavy spinning back kick which landed solidly to the body.
As McDonald faded, Barao gained strength and in the fourth round, he took over, pressing the action with strikes before changing levels and scoring a huge takedown just a minute into the round and quickly pouncing on McDonald's back during the ensuing scramble.
With "Mayday" fading, Barao aggressively pursued a submission, locking in an arm triangle and moving to side control to cinch the hold. McDonald held out as long as he could but after a period of resistance, he was forced to tap out.
For Michael McDonald, he did a great job of utilizing his grappling defensively to fend off Barao's early aggression on the canvas and escape to his feet, but his biggest mistake was failing to capitalize on the heavy shots he landed in the first round. He had Barao hurt after unloading a few good short rights hands on the inside along the fence and he allowed the champ to clear out the cobwebs and work for a takedown instead of punishing him with more blow that could have potentially finished the fight.
As the bout wore on, time was not on his side as he had never tasted a fourth round, which handed control back to the champion.
For Renan Barao, he was in control for most of the fight, other than the very end of the first round and the first half of the second. His striking was sharp and that left hook was finding a home whether he was leading with it or using it to counter McDonald's aggression. He did a great job of mixing up his attack with not only his punches and kicks but his takedowns, which always kept "Mayday" on his toes.
Barao also did a great job of surviving the early two rounds where McDonald was most dangerous and then really taking over as the fight entered the championship levels. Once in the fourth, it was obvious that McDonald wasn't the same fighter that started the bout while Barao still looked fresh. He initiated a scramble after a takedown attempt and pounced on an opening when McDonald briefly gave one, which allowed him to lock in an arm triangle choke and finish the fight.
With no clear-cut contender and after successfully defending his belt, Barao can now comfortably wait until the reigning champion Dominick Cruz is healthy enough to defend his title, as long as "The Dominator" doesn't have another setback in his rehab.