UK light-heavyweight Joshua Buatsi secured a victory yet disappointing debut to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a competitive 10-round bout at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective clean blows in a fight where the techniques failed to mesh, with constant grabbing spoiling the action.
The scoring judges scored it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my finest performance but what defines champions? They succeed," Buatsi stated in the ring as he was faced boos from the audience.
The Londoner got back to winning after his first professional defeat - an memorable fight with his previous opponent in February - to claim a twentieth professional win.
Some ringside observers felt the challenger, 31, deserved the victory but the Derbyshire fighter experienced the second setback of his 28-match professional journey.
The Champion Earns Victory in Dull Encounter
The fighter's advancement has slowed in the past few years through management issues and extended periods of lack of fights.
Previously predicted as the next star of UK boxing, he now is positioned trying to achieve expectations - possibly in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers prepared to take risks in a calculated opening few rounds.
The challenger, 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 bout at light heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for Buatsi, who worked behind a tight guard to narrowly win the cleaner periods.
The crowd's patience decreased because of frequent holding, with the challenger slipping to the canvas various instances during close exchanges.
Parker closed well, but several stanzas were hard to judge. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, awarding Buatsi just one round.
Buatsi moves on, but with the caliber of power puncher Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Memorial Motivates Manchester Derby Battle
In the co-main event, Arthur defeated Rea by close verdict in a terrific Manchester vs Manchester fight to capture the European light heavyweight belt.
The arena fell silent for a extremely emotional homage before the fight as ten bells sounded in memory of local hero Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast fight night in the city since Hatton's death. As the concluding sound faded, the silence transitioned to a chant of "only one Ricky Hatton".
The fighting within the ring reflected the emotion. The eventual winner was knocked down by a left hook flush on the jaw in the second round, standing uncertainly to his position on the count of eight.
But the traditional red shorts of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was marked up early, significant bruising appearing under his orbital area as the pair exchanged hard punches.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, responded in kind with powerful upward punches as the action rarely dropped over 12 rounds.
Arthur barely secured the result with official scores of draw, close margin and 115-112, but both fighters were determined and brave, all the qualities their inspiration Hatton embodied.
