UK light-heavyweight Joshua Buatsi earned a win yet unimpressive debut to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a close ten-round contest at the Co-op Live Arena.
But Parker found success, landing some telling individual punches in a fight where the techniques didn't complement each other, with excessive holding disrupting the fight.
Two judges judged it 96-94 to the winner, with the remaining official a even score.
"It wasn't my finest showing but how do champions respond? They succeed," the victor commented in the ring as he was met by disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Several boxing experts believed the challenger, 31, should have been awarded the decision but the Derbyshire fighter endured the second setback of his 28-bout professional journey.
The Champion Secures Victory in Dull Match
Buatsi's progress has stalled in recent years through promotional disputes and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now is positioned trying to realize his potential - possibly in what feels like a last chance - under new promotional backing.
He opened tentatively, with the two boxers willing to be aggressive in a tentative early stages.
Parker, whose sole prior loss came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was making just his second fight at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, causing problems for Buatsi, who utilized a solid defense to edge the better rounds.
The spectators' acceptance decreased during regular grabbing, with the challenger falling to the floor various instances during clinches.
Parker finished the stronger, but multiple periods were hard to judge. Although, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the presence of heavy hitter Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - on this evidence - still appears challenging.
Ricky Hatton Homage Inspires Manchester Derby Battle
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding local rivalry fight to secure the European light-heavyweight championship.
The stadium became quiet for a extremely emotional homage prior to the bout as 10 bells rang in memory of the city's native Ricky Hatton, who died aged 46 in last month.
It was the premier televised match card in the urban center since Hatton's death. As the concluding sound ended, the quiet gave way to a chant of "there's just one Ricky Hatton".
The fighting inside the ropes reflected the emotion. Arthur was knocked down by a powerful punch directly to the jaw in the initial stage, standing uncertainly to his position on the referee's count.
But the Manchester United-red equipment of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was marked up soon, significant bruising developing under his eye as the fighters exchanged powerful shots.
Rea, 27, connected with strong blows but the champion, 34, fought fire with fire with stinging uppercuts as the pace rarely dropped over the full distance.
Arthur narrowly won the decision with scoring tallies of even score, 115-113 and clearer margin, but both fighters were relentless and brave, everything their hero Hatton embodied.
