UK light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a competitive ten-round bout at the boxing arena.
But Parker found success, landing some telling clean blows in a match where the approaches never quite clicked, with frequent clinching spoiling the contest.
Two judges had it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my greatest showing but what defines champions? They succeed," the victor said in the ring as he was greeted with negative reactions from the spectators.
The Londoner bounced back after his maiden career setback - an memorable fight with Callum Smith in February - to earn a 20th career victory.
Some ringside observers believed the challenger, 31, deserved the victory but the contender experienced the second loss of his 28-bout career.
Buatsi Claims Win in Uneventful Affair
His career development has stalled in recent times through contract problems and extended periods of lack of fights.
Previously predicted as the next star of UK boxing, he now stands trying to fulfil that early promise - perhaps in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with the two boxers willing to be aggressive in a cagey early stages.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after breaking his hand during the bout, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who worked behind a tight guard to barely take the cleaner periods.
The audience's tolerance diminished amid regular grabbing, with the challenger falling to the floor various instances during grappling.
The underdog ended stronger, but multiple periods were difficult to score. Nevertheless, former world champion Carl Frampton - working with Dazn - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor moves on, but with the caliber of power puncher Benavidez, and Russian champion Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Hatton Memorial Motivates Manchester Derby Fight
In the supporting bout, Lyndon Arthur overcame Rea by close verdict in a excellent all-Manchester battle to win the continental title.
The stadium became quiet for a deeply poignant memorial before the fight as 10 bells tolled in honor of the city's native Hatton, who succumbed at age 46 in September.
It was the premier televised fight night in the location since the passing of Hatton. As the final chime ended, the stillness transitioned to a shout of "there's only one Ricky Hatton".
The action during the bout reflected the emotion. Arthur was floored by a powerful punch flush on the jaw in the initial stage, getting up unsteadily to his position on the eight count.
But the red-colored attire of Arthur soon came forward again. From the other corner, the opponent - in competitive blue - was injured early, significant bruising appearing under his eye as the fighters landed punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace seldom decreased over the full distance.
Arthur barely secured the verdict with official scores of even score, narrow lead and 115-112, but both fighters were determined and brave, everything their hero Hatton represented.
