UK light heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a split decision in a tight 10-round bout at the boxing arena.
But the challenger had his moments, landing some telling single shots in a match where the approaches failed to mesh, with excessive holding marring the contest.
The officials scored it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my best display but how do champions respond? They succeed," Buatsi stated in the arena as he was faced boos from the crowd.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to claim a 20th pro success.
Several boxing experts thought Parker, 31, should have been awarded the victory but the Derbyshire fighter suffered the second defeat of his 28-match career.
The Champion Earns Victory in Uneventful Encounter
The fighter's advancement has slowed in recent times through management issues and considerable time of inactivity.
Earlier forecast as the next star of the British fight scene, he now stands trying to fulfil that early promise - perhaps in what feels like a last chance - under fresh management.
He opened tentatively, with neither fighter ready to be aggressive in a calculated early stages.
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 mid-fight, was competing in only his second bout at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, causing problems for the favorite, who worked behind a solid defense to narrowly win the better periods.
The crowd's patience decreased amid regular grabbing, with the challenger going down several times during grappling.
Parker ended stronger, but multiple periods were hard to judge. However, previous titleholder Carl Frampton - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
Buatsi advances, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Homage Inspires Manchester Derby Battle
In the secondary fight, Lyndon Arthur defeated Bradley Rea by divided decision in a terrific Manchester vs Manchester contest to secure the continental belt.
The arena grew hushed for a deeply poignant homage before the fight as a bell ceremony tolled in remembrance of Manchester's own Hatton, who died aged 46 in September.
It was the first major televised boxing event in the city since the passing of Hatton. As the last bell disappeared, the stillness became a chant of "there's just one Hatton".
The action inside the ropes reflected the feeling. The eventual winner was sent to the canvas by a left hook flush on the jaw in the second round, getting up unsteadily to his position on the referee's count.
But the red-colored equipment of Arthur soon came forward again. Across the ring, the opponent - in competitive blue - was damaged early, significant bruising appearing under his face as the duo landed hard punches.
The challenger, 27, delivered effective strikes but Arthur, 34, responded in kind with effective uppercuts as the action rarely dropped over twelve rounds.
The victor barely secured the result with scoring tallies of 114-114, 115-113 and 115-112, but the two athletes were determined and courageous, everything their hero Hatton represented.
