British light-heavyweight Joshua Buatsi made a winning yet unimpressive beginning to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a split decision in a close 10-round contest at the Manchester venue.
But the challenger had his moments, connecting with powerful individual punches in a match where the styles failed to mesh, with excessive holding spoiling the fight.
The officials judged it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my finest display but what defines champions? They succeed," the victor commented in the ring as he was met by boos from the spectators.
The British fighter bounced back after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a twentieth professional win.
Various analysts believed the challenger, 31, should have been awarded the win but the British boxer experienced the second setback of his 28-bout professional journey.
Buatsi Earns Victory in Slow Encounter
The fighter's advancement has slowed in recent times through management issues and considerable time of inactivity.
Previously predicted as the next star of the British fight scene, he now stands trying to realize his potential - possibly in what seems like a final roll of the dice - under recent support.
He began cautiously, with neither fighter willing to take risks in a tentative early stages.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was making just his second bout at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for the favorite, who utilized a solid defense to barely take the better rounds.
The audience's tolerance decreased amid frequent holding, with the challenger falling to the floor multiple occasions during grappling.
Parker ended stronger, but many rounds were difficult to score. Although, previous titleholder Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, scoring for Buatsi just a single round.
The victor progresses, but with the likes of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Motivates Manchester Derby Contest
In the co-main event, Lyndon Arthur defeated Rea by split-decision in a terrific all-Manchester fight to win the continental title.
The venue fell silent for a profoundly moving memorial before the fight as a bell ceremony tolled in memory of local hero Ricky Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast boxing event in the urban center since Hatton's passing. As the concluding sound ended, the silence became a roar of "there's only one Ricky Hatton".
The fighting within the ring matched the feeling. Arthur was sent to the canvas by a powerful punch directly to the jaw in the initial stage, rising shakily to his footing on the count of eight.
But the red-colored equipment of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was marked up early, significant bruising appearing under his orbital area as the duo traded hard punches.
Rea, 27, connected with strong blows but Arthur, thirty-four, responded in kind with powerful upward punches as the action hardly diminished over 12 rounds.
The victor narrowly won the verdict with judges scorecards of draw, 115-113 and wider gap, but both fighters were determined and full of heart, all the qualities their hero Hatton represented.
