UK light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a tight ten-round contest at the Manchester venue.
But the challenger landed significant shots, landing some telling clean blows in a match where the techniques never quite clicked, with frequent clinching marring the contest.
Two judges had it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my finest display but what do champions do? They win," Buatsi said in the ringside as he was met by disapproval from the crowd.
The Londoner got back to winning after his maiden career setback - an memorable fight with his previous opponent in last winter - to secure a twentieth professional win.
Various analysts believed the challenger, 31, deserved the decision but the contender experienced the second defeat of his 28-match career.
The Champion Claims Triumph in Uneventful Encounter
Buatsi's progress has stalled in recent years through contract problems and extended periods of inactivity.
Earlier forecast as the next star of UK boxing, he now stands trying to realize his potential - maybe in what seems like a final roll of the dice - under fresh management.
He started carefully, with neither fighter prepared to be aggressive in a calculated opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was participating in his second bout at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a protective stance to edge the more effective periods.
The crowd's patience diminished because of constant clinching, with Parker falling to the floor multiple occasions during grappling.
Parker ended stronger, but multiple periods were difficult to score. Although, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the likes of heavy hitter Benavidez, and Russian champion Bivol ruling the division, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Motivates Local Rivalry Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by split-decision in a outstanding Manchester vs Manchester fight to win the European light-heavyweight belt.
The arena grew hushed for a profoundly moving homage prior to the bout as 10 bells tolled in remembrance of local hero Ricky Hatton, who died 46 years old in recently.
It was the first major televised boxing event in the location since Hatton's passing. As the last bell disappeared, the silence gave way to a roar of "there's just one Hatton".
The action within the ring equaled the emotion. The eventual winner was knocked down by a powerful punch directly to the chin in the initial stage, getting up unsteadily to his footing on the count of eight.
But the traditional red attire of the fighter soon came forward again. Across the ring, the opponent - in competitive blue - was injured early, heavy swelling developing under his orbital area as the pair traded powerful shots.
Rea, 27, landed power punches but Arthur, thirty-four, matched the intensity with stinging uppercuts as the action rarely dropped over the full distance.
Arthur edged the result with official scores of even score, close margin and wider gap, but both fighters were determined and full of heart, exactly what their idol Hatton stood for.
