Conor McGregor, right, embraces Jerry Cerrone, the grandmother of Donald “Cowboy” Cerrone, after a UFC 246 welterweight mixed martial arts bout on Saturday night in Las Vegas. (AP photo)

LAS VEGAS — Conor McGregor’s opening flurry — a punch that missed, followed by shoulder and elbow shots to the face — bloodied Donald Cerrone’s nose. He then floored Cerrone only 20 seconds into the bout with a perfectly placed kick to the head, and he mercilessly finished on the ground.

When he paraded around the ring with an Irish flag on his shoulders to celebrate, the mixed martial arts world knew McGregor is back with a big bang.

The Irish former two-division champion came out of a three-year stretch of relative inactivity and outside-the-cage troubles with a welterweight performance in UFC 246 on Saturday night that echoed his greatest fights during his unparalleled rise.

“I feel really good, and I came out of here unscathed,” McGregor said. “I’m in shape. We’ve got work to do to get back to where I was.”

After hurting Cerrone (36-14) with his first punch, McGregor (22-4) dropped him with a sublime kick to the jaw. McGregor pounced and forced referee Herb Dean to save Cerrone, delighting a sellout crowd of 19,040 at T-Mobile Arena.

McGregor’s hand hadn’t been raised in victory since November 2016, when he stopped lightweight Eddie Alvarez to become the first fighter in UFC history to hold two championship belts simultaneously. With his fame and fortune multiplying, McGregor fought only his boxing match with Floyd Mayweather in 2017, and he lost a one-sided UFC bout to lightweight champion Khabib Nurmagomedov in late 2018.

After a year spent out of competition and in repeated trouble with the law, McGregor got back into training and vowed to return.