UK light heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a close 10-round fight at the Manchester venue.
But Parker had his moments, connecting with powerful clean blows in a fight where the techniques didn't complement each other, with frequent clinching spoiling the fight.
Two judges judged it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my best display but what do champions do? They prevail," the victor commented in the arena as he was greeted with boos from the spectators.
The Londoner got back to winning after his initial pro loss - an epic battle with his previous opponent in February - to secure a twentieth professional win.
Several boxing experts believed the challenger, 31, deserved the decision but the British boxer experienced the second loss of his 28-fight career.
The Champion Secures Victory in Dull Affair
Buatsi's progress has stalled in recent times through management issues and extended periods of inactivity.
Previously predicted as the future of British boxing, he now stands trying to fulfil that early promise - maybe in what appears to be a ultimate opportunity - under recent support.
He opened tentatively, with the two boxers willing to take risks in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against his former opponent in 2022 after damaging his hand during the bout, was making just his second fight at the higher weight class.
By the middle rounds, the underdog had stayed in contention, creating difficulties for Buatsi, who worked behind a tight guard to narrowly win the cleaner stanzas.
The audience's tolerance decreased amid frequent holding, with the challenger going down various instances during close exchanges.
Parker finished the stronger, but many rounds were difficult to score. However, former world champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
The victor progresses, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Hatton Memorial Inspires All-Manchester Battle
In the co-main event, Lyndon Arthur beat Rea by split-decision in a outstanding Manchester vs Manchester battle to secure the continental championship.
The venue grew hushed for a extremely emotional tribute prior to the bout as 10 bells sounded in remembrance of the city's native Hatton, who passed away at age 46 in last month.
It was the premier televised fight night in the city since Hatton's death. As the final chime disappeared, the quiet became a roar of "there's just one Ricky Hatton".
The fighting inside the ropes reflected the sentiment. The eventual winner was knocked down by a significant blow directly to the chin in the early round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red shorts of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was damaged soon, noticeable damage appearing under his eye as the duo landed powerful shots.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity hardly diminished over twelve rounds.
The victor narrowly won the result with judges scorecards of draw, 115-113 and wider gap, but each competitor were determined and full of heart, everything their hero the legend stood for.
