BOSTON — Beneath 23 championship banners in the TD Garden champions Daniel Cormier and Stipe Miocic retained their titles at UFC 220 on Saturday night.

The main event witnessed perhaps the most exciting opening round in UFC heavyweight championship history, with both Stipe Miocic and Francis Ngannou landing big shots and the champion landing three takedowns. The underdog Ohioan not only dodged looping punches but scored the more effective strikes. The pace slowed in the second, with Miocic using takedowns to wear down his exhausted opponent.

In the third, a mouth-open, arms-down Ngannou nevertheless nailed Miocic with a shot only for the champ to successfully shoot for another takedown. His ground-and-pound from top position inflicts damage and saps more energy from the drained Cameroonian.

Twenty seconds into the fourth, Miocic again tackles the challenger to the mat. Even when Miocic seemingly lets him loose, a listless Ngannou cannot get loose. Against the fence and on Ngannou’s back, the champion pounds away with Herb Dean looking on intently and the challenger, down four rounds to zero, not fighting back.

In the fifth, the champion grinds the challenger against the fence. Ngannou threatens with a choke but Miocic escapes. Halfway through the round, Herb Dean separates the men to the delight of the crowd. But Ngannou looks like a zombie, stumbling around the octagon without purpose or energy.

The judges unanimously scored the bout 50-44 for the underdog champion who made his record third defense against the odds and the oddsmakers.

In the co-main event, Daniel Cormier landed several looping shots to hurt Volkan Oezdemir in the closing two minutes of the opening round before ending the round with a rear-naked choke stopped by the horn. A takedown less than a minute into the second round put the light heavyweight champion in side control, from where he secured a crucifix that allowed him to unleash vicious ground-and-pound that made a stoppage a formality.

“I’ve been through a lot,” Cormier explained after the win. “I go through a lot because of my greatest rival, but it feels good to get back in here and get a victory. I’ve lost twice to Jon Jones. I said coming in here that I felt like I was fighting for a vacant title again. I got the job done, so I’m the UFC champion again.”

The Boston crowd, which essentially adopted Cormier as an honorary local, treated the successful title defense with explosive enthusiasm.  Cormier improved to 20-1 while his Swiss opponent dropped to 15-2.

On the main card’s opener, bantamweight Rob Font kicked, punched, and hammerfisted his way to an upset second-round stoppage of Thomas Almeida at 2:24 of a second round that witnessed the local hero send the Brazilian summersaulting before ultimately sending him to the showers.

The Boston Finisher lived up to nickname by ending Shane Burgos’s night 32 seconds into the third round. Calvin Kattar split the first two rounds of the entertaining scrap with his featherweight opponent before a right sent Burgos stumbling, an uppercut put him down, and a flurry of strikes on the grounded opponent forced him back to the locker room with the encouragement of the referee.

On the undercard, highlight-reel true knockouts by Islam Makhachev of Gleison Tibau and Abdul Razak Alhassan of Sabah Homasi dropped jaws in the arena and at home.