UK light heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a split decision in a competitive ten-round fight at the Co-op Live Arena.
But the challenger found success, connecting with powerful single shots in a contest where the approaches didn't complement each other, with constant grabbing disrupting the action.
The scoring judges scored it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They succeed," the victor stated in the ring as he was faced disapproval from the spectators.
The Londoner bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to claim a 20th career victory.
Various analysts felt the challenger, thirty-one, deserved the win but the British boxer experienced the second setback of his 28-bout career.
The Champion Earns Triumph in Slow Match
The fighter's advancement has stalled in recent times through contract problems and long spells of inactivity.
Once tipped as the rising talent of the British fight scene, he now finds himself trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter ready to overcommit in a tentative early stages.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in 2022 after suffering a hand injury mid-fight, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for Buatsi, who worked behind a protective stance to narrowly win the cleaner stanzas.
The crowd's patience wore thin during frequent holding, with the challenger falling to the floor multiple occasions during close exchanges.
Parker finished the stronger, but many rounds were hard to judge. Although, previous titleholder Carl Frampton - commentating on Dazn - had it particularly wide for Parker, awarding Buatsi just only one stanza.
Buatsi advances, but with the likes of power puncher David Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - based on this performance - still looks steep.
Hatton Tribute Motivates All-Manchester Contest
In the supporting bout, Lyndon Arthur overcame Rea by split-decision in a outstanding all-Manchester fight to win the European light heavyweight championship.
The venue grew hushed for a deeply poignant memorial prior to the bout as a bell ceremony rang in honor of Manchester's own Ricky Hatton, who passed away at age 46 in recently.
It was the first major televised fight night in the city since the passing of Hatton. As the concluding sound faded, the silence became a shout of "there's only one Hatton".
The action during the bout matched the sentiment. The eventual winner was knocked down by a left hook squarely on the jaw in the early round, rising shakily to his feet on the count of eight.
But the Manchester United-red attire of the fighter soon pressed ahead again. From the other corner, Rea - in opposing blue - was damaged early, significant bruising developing under his orbital area as the fighters traded hard punches.
Rea, 27, connected with strong blows but the champion, thirty-four, matched the intensity with effective uppercuts as the pace hardly diminished over 12 rounds.
The victor edged the decision with judges scorecards of 114-114, narrow lead and clearer margin, but both fighters were relentless and courageous, all the qualities their hero Hatton embodied.
