UK light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a competitive ten-round contest at the Manchester venue.
But Parker landed significant shots, landing some telling clean blows in a match where the approaches never quite clicked, with constant grabbing marring the contest.
The officials judged it 96-94 for to Buatsi, with the third a even score.
"It wasn't my best showing but how do champions respond? They win," the victor stated in the ring as he was faced boos from the crowd.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in February - to claim a twentieth professional win.
Several boxing experts thought Parker, thirty-one, should have been awarded the victory but the contender endured the second setback of his 28-bout career.
Buatsi Secures Triumph in Dull Match
The fighter's advancement has slowed in recent years through management issues and long spells of lack of fights.
Previously predicted as the future of the British fight scene, he now stands trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with neither fighter ready to be aggressive in a tentative opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in two years ago after breaking his hand during the bout, was making just his second fight at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for Buatsi, who utilized a tight guard to edge the more effective rounds.
The spectators' acceptance wore thin amid regular grabbing, with Parker slipping to the canvas several times during close exchanges.
Parker finished the stronger, but many rounds were difficult to score. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just one round.
Buatsi progresses, but with the presence of heavy hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Memorial Motivates Local Rivalry Battle
In the co-main event, Arthur beat Rea by divided decision in a outstanding local rivalry battle to capture the continental championship.
The stadium fell silent for a profoundly moving homage before the fight as 10 bells tolled in remembrance of local hero Ricky Hatton, who succumbed 46 years old in recently.
It was the premier televised boxing event in the location since Hatton's death. As the final chime ended, the silence became a roar of "there's only one Hatton".
The competition during the bout reflected the sentiment. The eventual winner was sent to the canvas by a left hook flush on the face in the second round, standing uncertainly to his footing on the count of eight.
But the red-colored equipment of the fighter soon advanced again. On the opposite side, Rea - in rival City blue - was injured quickly, heavy swelling forming under his orbital area as the pair exchanged hard punches.
Rea, 27, landed power punches but the champion, thirty-four, fought fire with fire with stinging uppercuts as the intensity hardly diminished over 12 rounds.
The victor edged the decision with official scores of 114-114, 115-113 and wider gap, but both fighters were persistent and courageous, all the qualities their idol the legend embodied.
