British light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a close ten-round fight at the boxing arena.
But Parker landed significant shots, landing some telling clean blows in a contest where the approaches failed to mesh, with constant grabbing disrupting the contest.
The officials judged it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest performance but what defines champions? They win," Buatsi commented in the ringside as he was greeted with boos from the audience.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to claim a 20th pro success.
Several boxing experts believed Parker, thirty-one, deserved the decision but the Derbyshire fighter experienced the second defeat of his 28-bout professional journey.
The Champion Secures Triumph in Dull Match
His career development has stalled in recent times through promotional disputes and long spells of lack of fights.
Previously predicted as the future of UK boxing, he now stands trying to realize his potential - maybe in what seems like a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter prepared to be aggressive in a tentative opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after suffering a hand injury in the contest, was competing in only his second fight at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who operated with a protective stance to narrowly win the cleaner stanzas.
The audience's tolerance diminished during frequent holding, with Parker going down multiple occasions during clinches.
Parker finished the stronger, but multiple periods were challenging to assess. Nevertheless, former world champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, awarding Buatsi just only one stanza.
Buatsi advances, but with the presence of hard hitter Benavidez, and Russian star Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Hatton Tribute Fuels Manchester Derby Fight
In the secondary fight, Arthur overcame Rea by divided decision in a terrific Manchester vs Manchester battle to capture the European light heavyweight championship.
The stadium fell silent for a extremely emotional memorial prior to the bout as 10 bells sounded in remembrance of Manchester's own Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the final chime disappeared, the silence became a shout of "there's only one Ricky Hatton".
The fighting during the bout reflected the emotion. Arthur was knocked down by a powerful punch directly to the jaw in the second round, rising shakily to his position on the eight count.
But the traditional red attire of Arthur soon came forward again. Across the ring, the opponent - in rival City blue - was marked up soon, noticeable damage forming under his eye as the fighters traded hard punches.
The challenger, 27, connected with strong blows but the champion, 34, matched the intensity with effective uppercuts as the action hardly diminished over the full distance.
The victor edged the decision with official scores of 114-114, close margin and 115-112, but the two athletes were relentless and full of heart, all the qualities their idol Hatton embodied.
