UK light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to his career under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a split decision in a competitive ten-round bout at the Manchester venue.
But the challenger found success, connecting with powerful single shots in a contest where the styles didn't complement each other, with constant grabbing spoiling the contest.
The officials scored it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my finest showing but how do champions respond? They win," the victor commented in the ringside as he was met by disapproval from the audience.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to secure a 20th career victory.
Some ringside observers believed Parker, thirty-one, should have been awarded the decision but the contender suffered the second setback of his 28-fight professional journey.
Buatsi Earns Victory in Dull Affair
His career development has slowed in recent years through promotional disputes and long spells of lack of fights.
Once tipped as the rising talent 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 opened tentatively, with both competitors prepared to take risks in a cagey early stages.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was participating in his second appearance at the higher weight class.
By the halfway stage, Parker had kept it close, creating difficulties for Buatsi, who operated with a tight guard to barely take the cleaner stanzas.
The audience's tolerance wore thin during regular grabbing, with the challenger falling to the floor multiple occasions during grappling.
Parker finished the stronger, but several stanzas were hard to judge. Although, ex-champion the boxing analyst - commentating on Dazn - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor advances, but with the presence of heavy hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Memorial Inspires All-Manchester Contest
In the secondary fight, Lyndon Arthur defeated Rea by split-decision in a terrific Manchester vs Manchester battle to capture the European light heavyweight title.
The stadium became quiet for a profoundly moving tribute prior to the bout as ten bells rang in remembrance of local hero Hatton, who died 46 years old in last month.
It was the premier televised fight night in the location since Hatton's death. As the final chime faded, the silence became a chant of "only one Ricky Hatton".
The action inside the ropes matched the feeling. The eventual winner was sent to the canvas by a significant blow directly to the face in the early round, rising shakily to his feet on the eight count.
But the traditional red attire of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was marked up early, significant bruising appearing under his face as the pair exchanged hard punches.
The challenger, 27, delivered effective strikes but Arthur, 34, matched the intensity with stinging uppercuts as the action hardly diminished over the full distance.
The victor narrowly won the verdict with judges scorecards of draw, 115-113 and clearer margin, but the two athletes were persistent and courageous, exactly what their idol the legend embodied.
