UK light-heavyweight Joshua Buatsi made a winning yet underwhelming start to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a majority decision in a tight ten-round bout at the boxing arena.
But the challenger had his moments, delivering effective clean blows in a contest where the styles failed to mesh, with frequent clinching spoiling the action.
Two judges scored it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my finest performance but what defines champions? They succeed," Buatsi stated in the ring as he was met by boos from the audience.
The Londoner bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Several boxing experts thought Parker, thirty-one, should have been awarded the victory but the Derbyshire fighter experienced the second defeat of his 28-bout professional journey.
Buatsi Claims Victory in Dull Affair
The fighter's advancement has stalled in recent times through management issues and considerable time of inactivity.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors ready to overcommit in a tentative opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in 2022 after suffering a hand injury during the bout, was competing in only his second bout at light heavyweight.
By the middle rounds, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to narrowly win the better periods.
The audience's tolerance decreased because of constant clinching, with Parker slipping to the canvas multiple occasions during close exchanges.
Parker finished the stronger, but many rounds were difficult to score. However, previous titleholder the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the caliber of power puncher Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Homage Inspires Manchester Derby Battle
In the supporting bout, Arthur beat Rea by close verdict in a outstanding local rivalry fight to secure the continental title.
The arena fell silent for a profoundly moving memorial before the fight as a bell ceremony rang in honor of local hero Hatton, who passed away 46 years old in recently.
It was the first major televised fight night in the city since Hatton's death. As the final chime faded, the stillness became a shout of "only one Hatton".
The competition inside the ropes reflected the emotion. The eventual winner was floored by a powerful punch directly to the face in the early round, standing uncertainly to his footing on the eight count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. Across the ring, the opponent - in rival City blue - was injured quickly, significant bruising appearing under his eye as the pair landed punishing blows.
The challenger, 27, connected with strong blows but Arthur, 34, fought fire with fire with effective uppercuts as the action seldom decreased over the full distance.
Arthur narrowly won the result with scoring tallies of draw, narrow lead and 115-112, but each competitor were relentless and courageous, exactly what their inspiration Hatton represented.
