British light-heavyweight Joshua Buatsi made a winning yet unimpressive debut to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a majority decision in a close ten-round bout at the Manchester venue.
But the challenger had his moments, delivering effective clean blows in a fight where the techniques failed to mesh, with frequent clinching spoiling the action.
The scoring judges scored it 96-94 for to the winner, with the final judge a 95-95.
"It wasn't my best performance but how do champions respond? They succeed," Buatsi said in the ring as he was greeted with disapproval from the spectators.
The British fighter bounced back after his maiden career setback - an epic battle with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts believed Parker, 31, should have been awarded the decision but the contender endured the second loss of his 28-bout professional journey.
The Champion Secures Victory in Slow Encounter
The fighter's advancement has slowed in recent times through contract problems and long spells of inactivity.
Once tipped as the next star of British boxing, he now finds himself trying to realize his potential - perhaps in what seems like a last chance - under new promotional backing.
He opened tentatively, with both competitors willing to take risks in a calculated early stages.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after damaging his hand during the bout, was participating in his second fight at light heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who operated with a tight guard to barely take the more effective stanzas.
The audience's tolerance wore thin during frequent holding, with Parker going down various instances during close exchanges.
The underdog ended stronger, but many rounds were challenging to assess. Nevertheless, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, giving Buatsi just one round.
Buatsi advances, but with the presence of hard hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - based on this performance - still seems difficult.
Hatton Tribute Motivates Manchester Derby Battle
In the secondary fight, Arthur defeated Rea by close verdict in a excellent all-Manchester battle to win the European light-heavyweight belt.
The arena fell silent for a deeply poignant homage before the fight as a bell ceremony rang in honor of the city's native Ricky Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast fight night in the city since Hatton's death. As the final chime ended, the silence transitioned to a roar of "only one Hatton".
The action within the ring equaled the feeling. Arthur was sent to the canvas by a left hook directly to the face in the second round, rising shakily to his feet on the referee's count.
But the traditional red attire of the fighter soon advanced again. On the opposite side, Rea - in opposing blue - was damaged quickly, noticeable damage forming under his eye as the duo landed powerful shots.
Rea, 27, landed power punches but Arthur, thirty-four, matched the intensity with powerful upward punches as the action rarely dropped over twelve rounds.
Arthur edged the decision with official scores of even score, close margin and 115-112, but both fighters were relentless and brave, all the qualities their idol the legend represented.
