UK light heavyweight Joshua Buatsi secured a victory yet disappointing start to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a split decision in a close 10-round fight at the Manchester venue.
But Parker found success, landing some telling single shots in a match where the approaches never quite clicked, with excessive holding marring the contest.
The scoring judges judged it 96-94 to Buatsi, with the third a even score.
"It wasn't my best display but what defines champions? They succeed," the victor said in the arena as he was faced negative reactions from the crowd.
The Londoner got back to winning after his initial pro loss - an memorable fight with Callum Smith in last winter - to earn a 20th career victory.
Some ringside observers believed the challenger, thirty-one, should have been awarded the win but the Derbyshire fighter suffered the second defeat of his 28-fight career.
The Champion Claims Victory in Uneventful Match
Buatsi's progress has plateaued in recent years through management issues and considerable time of lack of fights.
Once tipped as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a final roll of the dice - under recent support.
He started carefully, with neither fighter prepared to overcommit in a cagey opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after damaging his hand mid-fight, was making just his second fight at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for the favorite, who utilized a tight guard to edge the better stanzas.
The crowd's patience wore thin during constant clinching, with the challenger slipping to the canvas various instances during grappling.
The underdog ended stronger, but several stanzas were difficult to score. Nevertheless, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just one round.
Buatsi moves on, but with the caliber of hard hitter Benavidez, and Russian star Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Tribute Fuels All-Manchester Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding Manchester vs Manchester contest to secure the continental championship.
The arena grew hushed for a deeply poignant homage ahead of the contest as a bell ceremony rang in honor of Manchester's own Ricky Hatton, who passed away at age 46 in September.
It was the first major televised boxing event in the city since the passing of Hatton. As the final chime ended, the silence gave way to a roar of "there's just one Hatton".
The competition within the ring matched the sentiment. The eventual winner was floored by a left hook directly to the chin in the second round, rising shakily to his feet on the eight count.
But the Manchester United-red attire of the fighter soon advanced again. Across the ring, Rea - in rival City blue - was injured soon, heavy swelling developing under his eye as the fighters traded punishing blows.
Rea, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with stinging uppercuts as the action seldom decreased over twelve rounds.
Arthur edged the verdict with judges scorecards of draw, narrow lead and clearer margin, but each competitor were persistent and courageous, everything their hero the legend represented.
