UK light heavyweight Joshua Buatsi earned a win yet unimpressive beginning to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a close 10-round bout at the Manchester venue.
But Parker found success, landing some telling single shots in a contest where the techniques never quite clicked, with constant grabbing marring the action.
Two judges scored it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my finest showing but what defines champions? They win," the victor commented in the ring as he was greeted with boos from the audience.
The Londoner returned to winning ways after his first professional defeat - an epic battle with Callum Smith in February - to claim a twentieth professional win.
Several boxing experts believed the challenger, thirty-one, deserved the victory but the British boxer experienced the second loss of his 28-bout career.
Buatsi Secures Victory in Uneventful Affair
His career development has stalled in the past few years through promotional disputes and extended periods of lack of fights.
Once tipped as the rising talent of British boxing, he now stands trying to realize his potential - perhaps in what seems like a ultimate opportunity - under recent support.
He opened tentatively, with neither fighter willing to take risks in a tentative initial rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was making just his second fight at light heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for Buatsi, who worked behind a solid defense to narrowly win the better periods.
The spectators' acceptance diminished during constant clinching, with the challenger going down multiple occasions during clinches.
The underdog finished the stronger, but several stanzas were challenging to assess. However, former world champion the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the caliber of hard hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - on this evidence - still appears challenging.
Hatton Memorial Inspires Manchester Derby Contest
In the secondary fight, Arthur overcame Rea by split-decision in a terrific local rivalry fight to win the European light-heavyweight belt.
The stadium fell silent for a deeply poignant homage ahead of the contest as ten bells sounded in memory of the city's native Ricky Hatton, who passed away 46 years old in September.
It was the premier televised fight night in the location since the passing of Hatton. As the final chime faded, the silence gave way to a shout of "there's only one Hatton".
The action within the ring matched the sentiment. The eventual winner was floored by a powerful punch directly to the jaw in the initial stage, rising shakily to his footing on the eight count.
But the red-colored equipment of Arthur soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was injured soon, heavy swelling developing under his orbital area as the fighters traded powerful shots.
The challenger, 27, landed power punches but the champion, 34, fought fire with fire with powerful upward punches as the action hardly diminished over twelve rounds.
The victor narrowly won the verdict with official scores of draw, close margin and clearer margin, but the two athletes were relentless and full of heart, exactly what their hero the legend embodied.
