UK light-heavyweight Joshua Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a split decision in a competitive 10-round fight at the Manchester venue.
But the challenger landed significant shots, connecting with powerful clean blows in a match where the techniques didn't complement each other, with frequent clinching marring the action.
The scoring judges scored it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my finest performance but what defines champions? They prevail," Buatsi stated in the ringside as he was faced negative reactions from the crowd.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in last winter - to claim a 20th pro success.
Some ringside observers thought Parker, 31, deserved the decision but the contender endured the second setback of his 28-bout professional journey.
The Champion Secures Triumph in Uneventful Affair
The fighter's advancement has plateaued in recent years through management issues and considerable time of lack of fights.
Once tipped as the next star of British boxing, he now finds himself trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with the two boxers willing to overcommit in a tentative opening few rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second bout at light heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for the favorite, who utilized a solid defense to edge the better periods.
The spectators' acceptance decreased amid frequent holding, with Parker going down several times during grappling.
The underdog ended stronger, but multiple periods were challenging to assess. However, former world champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, giving Buatsi just only one stanza.
The victor progresses, but with the caliber of hard hitter Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Hatton Memorial Inspires Manchester Derby Battle
In the supporting bout, Lyndon Arthur overcame Bradley Rea by split-decision in a outstanding Manchester vs Manchester contest to capture the European light heavyweight belt.
The stadium became quiet for a deeply poignant tribute ahead of the contest as ten bells rang in honor of local hero Hatton, who passed away 46 years old in September.
It was the premier televised fight night in the urban center since Hatton's death. As the final chime disappeared, the silence became a shout of "there's just one Ricky Hatton".
The competition during the bout reflected the emotion. Arthur was knocked down by a powerful punch squarely on the chin in the second round, getting up unsteadily to his position on the count of eight.
But the traditional red attire of Arthur soon came forward again. Across the ring, Rea - in rival City blue - was damaged early, heavy swelling appearing under his orbital area as the duo exchanged powerful shots.
The challenger, 27, landed power punches but the champion, 34, fought fire with fire with powerful upward punches as the pace seldom decreased over 12 rounds.
The victor edged the result with scoring tallies of 114-114, 115-113 and clearer margin, but both fighters were persistent and courageous, exactly what their hero the legend embodied.
