British light-heavyweight Joshua Buatsi earned a win yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a competitive 10-round bout at the Co-op Live Arena.
But the challenger had his moments, landing some telling individual punches in a fight where the approaches failed to mesh, with frequent clinching marring the contest.
The scoring judges had it 96-94 for to the winner, with the third a even score.
"It wasn't my best showing but how do champions respond? They win," the victor stated in the ringside as he was faced disapproval from the audience.
The British fighter bounced back after his first professional defeat - an memorable fight with Callum Smith in last winter - to secure a 20th career victory.
Several boxing experts thought Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter experienced the second loss of his 28-match career.
The Champion Earns Win in Dull Encounter
The fighter's advancement has stalled in the past few years through management issues and considerable time of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under fresh management.
He started carefully, with neither fighter prepared to be aggressive in a cagey initial rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was participating in his second bout at light heavyweight.
By the halfway stage, the underdog had stayed in contention, causing problems for Buatsi, who utilized a solid defense to edge the better stanzas.
The crowd's patience diminished amid frequent holding, with Parker going down several times during grappling.
The underdog finished the stronger, but many rounds were difficult to score. However, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the caliber of hard hitter Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Tribute Inspires All-Manchester Fight
In the co-main event, Lyndon Arthur beat Rea by divided decision in a outstanding Manchester vs Manchester battle to secure the continental belt.
The stadium became quiet for a profoundly moving memorial prior to the bout as 10 bells rang in honor of the city's native Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast fight night in the urban center since the passing of Hatton. As the final chime ended, the silence became a chant of "only one Hatton".
The fighting within the ring matched the emotion. The eventual winner was sent to the canvas by a significant blow flush on the chin in the early round, getting up unsteadily to his position on the eight count.
But the red-colored attire of Arthur soon advanced again. Across the ring, the opponent - in opposing blue - was damaged quickly, heavy swelling developing under his eye as the duo landed punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with stinging uppercuts as the action seldom decreased over the full distance.
Arthur edged the decision with scoring tallies of draw, narrow lead and wider gap, but both fighters were persistent and brave, everything their hero the legend represented.
