Seth Mitchell, here after a training session in June 2011, didn’t last beyond the second round in his fight with Johnathon Banks on Saturday night. (Mark Gail/THE WASHINGTON POST)

After his longest layoff since turning professional, Brandywine heavyweight Seth Mitchell lost for the first time on Saturday night, going down three times in the second round amid a barrage of combinations from Johnathon Banks before the fight at Boardwalk Hall was stopped at 2 minutes 37 seconds.

By the time referee Eddie Cotton intervened, Mitchell had absorbed the most punishment of his career. Now his aspirations to reclaim the heavyweight championship of the world for the United States are in serious jeopardy given Mitchell’s age (30) and stunningly flat showing in his 27th fight.

In the night’s co-main event to Mitchell vs. Banks, Adrien Broner knocked out Antonio DeMarco in the eighth round for the World Boxing Council lightweight championship. The card was the first at Boardwalk Hall since Superstorm Sandy ravaged Atlantic City on Oct. 29.

After Mitchell and Banks sized up one another in the first round, Banks advanced early in the second to connect with a left uppercut that wobbled Mitchell (25-1-1, 19 knockouts). Then Banks (29-1-1, 19 KOs) followed with a right jab that did more damage, and Mitchell soon fell to the canvas.

Another jab sent Mitchell down again, and when he landed on the canvas for a third time, Cotton stepped over him and waved both arms. Banks landed 25 of 42 power shots to just 11 of 43 for Mitchell, who connected on 29 percent of his punches. Banks, meanwhile, efficiently landed 49 percent of his 77 total punches.

“I could have got through the round, but the ref did what he had to do,” Mitchell said. “I’m good. I feel okay. He just caught me with a good shot. He dazed me, and I’m really upset.”

Known as a skilled counter-puncher, Banks was able to land his first major blow when Mitchell threw a right cross that missed. Banks quickly sent his left hand into Mitchell’s chin in what became the decisive punch of the bout.

Banks dedicated this fight to former trainer Emanuel Steward, who died last month of colon cancer, and was clearly emotional after the victory that allowed him to wrest the North American Boxing Organization title from Mitchell.

The last time Mitchell fought at this venue nearly seven months ago, he came close to going down in the first round against Chazz Witherspoon but retaliated strongly in the second round before finishing the job decisively in the third with his 10th consecutive knockout.

“It won’t spoil my dreams,” the former All-Met linebacker from Gwynn Park High said of his goal of facing unified heavyweight champion Wladimir Klitschko, “but it might set me back a little bit. Don’t feel sorry for me. Feel sorry for my next opponent.”

In the first bout on Saturday, White Plains, Md., lightweight Terron Grant dropped Abraham Esquivel three times before referee Earl Brown stopped the fight at 2:14 of the first round. The knockout also meant the Boys & Girls Club of Atlantic City, which suffered significant damage from Sandy, will receive a $3,000 donation provided by Golden Boy Promotions, Golden Boy President Oscar De La Hoya and Caesars Atlantic City.

“I did not know about the $3,000 going to the boys and girls clubs,” said Grant, who improved to 5-0. “It makes me feel real good for them to be blessed because I came out with the win. If I had $3,000, I would give it to them myself.”