Seth Mitchell, shown here in 2011, said one mistake led to his loss in November to Johnathon Banks. On Saturday, he’ll look to avenge that loss and continue his ascent up the heavyweight ranks. (Mark Gail/THE WASHINGTON POST)

With his eyes focused on the target and fists cocked in striking position, Seth Mitchell attacked the punching bag last week with such ferocity that the sound of the blows reverberated throughout the modest gym in Clinton where he has been training for the defining fight of his career.

There may be more meaningful bouts down the road, perhaps even an opportunity to claim the heavyweight championship of the world, but these days, all that matters for Mitchell is Saturday night’s shot at redemption against Johnathon Banks at Barclays Center in Brooklyn.

“I need to win the fight,” Mitchell said.

The Brandywine native has been consumed with this assignment since Banks sent him to the canvas three times during the second round of their first bout on Nov. 17 in Atlantic City. The final knockdown resulted in the first loss of Mitchell’s career and halted his ascent to the top of the division.

Heading into that fight, Mitchell (25-1-1, 19 knockouts) had been used to punishing opponents since his professional debut in January 2008. The former All-Met linebacker from Gwynn Park High School went on to win 24 of his next 25 fights, including the last 10 by knockout. Only one of those matches lasted beyond the third round.

Mitchell’s knockout power and expanding résumé had him on the fast track to a potential matchup against world heavyweight champion Vladimir Klitschko. No American has won a heavyweight world title since Shannon Briggs in 2006, and no U.S. fighter since Hasim Rahman in 2001 has owned multiple heavyweight belts.

But a moment of recklessness became Mitchell’s undoing at Boardwalk Hall seven months ago. That’s when he reached with his right hand, missing completely and allowing Banks an open window to counterpunch. The first offering from Banks dazed Mitchell, and a combination soon thereafter dropped him.

The victory was especially gratifying for Banks (29-1-1, 19 KOs) given that his beloved trainer, Emanuel Steward, had died less than a month earlier. Banks attended the Hall of Famer’s memorial service in Detroit only four days before the fight.

“Some people may say that I was hyped up over the death of Steward, that this was a fluke,” said Banks, who was seen as a heavy underdog. “It doesn’t bother me. I’ve heard it. I know what it was, and I know what it is. I don’t believe in flukes.”

Mitchell, meantime, said that one mistake — rather than a sweeping deficiency in his boxing acumen — was to blame for the sudden defeat. So shortly after decompressing in his dressing room that night, Mitchell turned to his team, including recently added adviser Al Haymon, to ask two questions.

The first was how much the loss had set him back. The second was when he could expect a rematch as stipulated in the fight contract.

“If Johnathon Banks would have outboxed me for six or seven rounds or outclassed me, of course the fighter in me would’ve wanted a rematch, but I would have taken the rematch right away,” Mitchell said. “I believe that I’m a better fighter than him, and I didn’t show everything that I’m capable of.”

Mitchell and Banks originally were scheduled to conduct their rematch Feb. 16 in Atlantic City as the co-headliner to Adrien Broner’s first lightweight title defense against Gavin Rees, but Banks’s K2 Promotions team revealed 10 days before the bout that the North American Boxing Organization champion had broken his thumb during training.

While Banks rested his thumb, Mitchell, 31, continued his fitness regimen uncertain when or even whether there would be a rematch. The sides eventually agreed to reschedule as part of Saturday’s card, in which Broner is set to face Paulie Malignaggi for Malignaggi’s World Boxing Association welterweight championship.

“He’s a warrior, and I didn’t believe for one second he was going to sit back and sulk and take a long hiatus,” said Sharif Salim, Mitchell’s manager. “I think right now what we’re seeing is the heart of a champion, that you can get knocked down and get back up, and that’s what he’s doing. He is showing that to us, and I think we’re in for a really good show.”