UK light heavyweight Joshua Buatsi earned a win yet disappointing debut to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive 10-round contest at the Co-op Live Arena.
But the challenger had his moments, delivering effective single shots in a match where the approaches didn't complement each other, with frequent clinching disrupting the action.
The scoring judges had it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my finest showing but how do champions respond? They prevail," Buatsi commented in the ringside as he was greeted with disapproval from the audience.
The British fighter got back to winning after his first professional defeat - an memorable fight with Callum Smith in February - to earn a 20th career victory.
Several boxing experts thought Parker, 31, should have been awarded the victory but the Derbyshire fighter endured the second defeat of his 28-match professional journey.
The Champion Claims Win in Dull Affair
The fighter's advancement has stalled in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to fulfil that early promise - perhaps in what seems like a ultimate opportunity - under new promotional backing.
He started carefully, with the two boxers willing to be aggressive in a calculated opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second fight at light-heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for the favorite, who operated with a tight guard to edge the better rounds.
The audience's tolerance wore thin during constant clinching, with the challenger falling to the floor various instances during grappling.
The underdog closed well, but multiple periods were hard to judge. Although, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for Parker, awarding Buatsi just one round.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Tribute Inspires Local Rivalry Contest
In the co-main event, Lyndon Arthur beat Rea by divided decision in a outstanding Manchester vs Manchester fight to capture the European light heavyweight belt.
The venue fell silent for a extremely emotional homage prior to the bout as 10 bells tolled in remembrance of Manchester's own Hatton, who passed away aged 46 in September.
It was the premier televised match card in the urban center since Hatton's passing. As the final chime ended, the silence transitioned to a chant of "there's just one Ricky Hatton".
The action during the bout reflected the emotion. Arthur was sent to the canvas by a significant blow directly to the face in the early round, getting up unsteadily to his position on the count of eight.
But the Manchester United-red equipment of the fighter soon came forward again. On the opposite side, Rea - in rival City blue - was damaged quickly, heavy swelling forming under his orbital area as the pair traded powerful shots.
Rea, 27, landed power punches but the champion, 34, responded in kind with powerful upward punches as the intensity hardly diminished over the full distance.
The victor narrowly won the verdict with official scores of even score, close margin and clearer margin, but both fighters were relentless and full of heart, all the qualities their hero Hatton embodied.
