Lucas Matthysse knocks down Lamont Peterson in the third round on his way to a TKO win during their fight in Atlantic City. (Al Bello/GETTY IMAGES)

District fighter Lamont Peterson came into Saturday night’s bout against Lucas Matthysse with a plan to measure his opponent in the early rounds and then outbox him the rest of the way at Boardwalk Hall.

Peterson never got that chance, falling victim to two stinging left hooks in the third that sent the International Boxing Federation junior welterweight champion to the canvas. That was enough for referee Steve Smoger, who stopped the non-title fight at 2 minutes 14 seconds in a result that has been typical for Matthysse.

The Argentine slugger logged the 32nd knockout of his career, this time overwhelming an opponent with a decorated résumé who had designs on joining the conversation for best pound-for-pound fighter in the world. Now it’s Matthysse whose stock is soaring given the excitement he brings into the ring with his one-punch power.

“I got a little lazy with my jab,” said Peterson, who suffered the first knockout of his career. “He hit me with some really good shots. I felt as if I could have kept going, but the ref called it. I guess tonight he was a better fighter.”

Peterson (31-2, 16 knockouts) went down three times in all. The first instance came late in the second round after Matthysse (34-2) connected with a straight right that dazed Peterson. Matthysse followed with a looping left hook, and Peterson was down for the fourth time in his last five fights.

The Washington Post’s Mike Wise makes the case that D.C. should get behind Lamont Peterson, who is competing for the International Boxing Federation’s title on Saturday. (Post Sports Live)

When Peterson hit the mat for the first time in Round 3, Smoger told him he would call the match after one more significant shot. Moments later the stunning end arrived for Peterson, who lost for the first time since Timothy Bradley beat him by decision on Dec. 12, 2009.

“I knew when I dropped him, I knew he could tell how strong I was,” Matthysse said through an interpreter. “Now we all know who the best 140-pound fighter is. No one has dominated Peterson like that.”

This scheduled 12-rounder at a catch weight of 141 pounds drew 4,215 at Boardwalk Hall, and was the rare matchup that generated buzz despite no belts being up for grabs. In his first appearance as a member of the Golden Boy Promotions stable of fighters, Peterson said leading up to the bout he would have preferred if his title were at stake along with Matthysse’s World Boxing Council interim super lightweight title.

But the IBF would not permit a unification involving an interim champion, and Matthysse wanted to keep his title rather than relinquish it and fight for only Peterson’s belt. Holding the interim title means Matthysse remains a mandatory challenger for Danny Garcia, who owns three belts at 140 pounds, including the WBC.

“I never imagined I was going to finish it that fast,” Matthysse said. Peterson is “a great champion. He’s a great fighter. He’s fought the best, and nobody ever has been able to knock him out.”

Garcia was among several of the top pound-for-pound fighters in the world observing close to ringside. Also in the crowd was Amir Khan, who lost to Peterson Dec. 10, 2011, in a 12-round split decision at Walter E. Washington Convention Center.

All of those fighters presumably are in the mix to face pound-for-pound king Floyd Mayweather in what would be a highly lucrative payday for any opponent. The highest paid athlete in the world banked $32 million in his last fight, handily beating Robert Guerrero via unanimous decision.

Peterson, 29, has spoken publicly about wanting to fight Mayweather, but Saturday’s outcome leaves his future as a viable headliner in serious doubt. With a possible match featuring Garcia and Matthysse in play for Verizon Center on Sept. 7, according to Golden Boy CEO Richard Schaefer, Peterson could be be a co-feature on that card, perhaps against Zab Judah.

“The game plan was to keep boxing,” Peterson said. “Sometime in the second round, he hit me in the back of the head. I got a little upset, started getting a little more reckless, wanted to bang. I could feel the fight heating up. I kind of abandoned the game plan a bit, and I paid for it.”

Note: Anthony Peterson, Lamont’s younger brother, also watched with great interest several hours after he dispatched Dominic Salcido in an undercard bout.

Anthony Peterson (32-1, 21 KOs) fought for the first time in 17 months, the longest such layoff of the lightweight’s career, anticipating perhaps a touch of rust in a scheduled 10-rounder. He wound up barely breaking a sweat, winning after the completion of Round 2 when the match was stopped because of Salcido’s broken nose.

A ringside doctor determined because the bone in Salcido’s nose was displaced, it potentially could cause more serious internal head trauma if he absorbed additional blows to the face.

That left Peterson with exactly 10 rounds of officially sanctioned boxing since Dec. 10, 2011, when he beat Daniel Attah via unanimous decision on the undercard of Lamont Peterson’s upset of Khan.

District light heavyweight Thomas Williams also won convincingly on Saturday’s undercard, scoring a unanimous decision against Otis Griffin. Two judges scored it 79-73, and another 80-72.