UK light heavyweight Joshua Buatsi secured a victory yet disappointing beginning to life under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a tight 10-round bout at the boxing arena.
But Parker landed significant shots, connecting with powerful single shots in a fight where the techniques didn't complement each other, with constant grabbing marring the contest.
The scoring judges judged it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my best showing but what do champions do? They prevail," Buatsi said in the ringside as he was faced disapproval from the audience.
The British fighter bounced back after his first professional defeat - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Several boxing experts felt the challenger, 31, deserved the decision but the British boxer suffered the second loss of his 28-bout professional journey.
The Champion Earns Win in Uneventful Match
His career development has stalled in the past few years through management issues and considerable time of inactivity.
Earlier forecast as the future of the British fight scene, he now stands trying to realize his potential - maybe in what appears to be a last chance - under fresh management.
He began cautiously, with both competitors prepared to take risks in a calculated opening few rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand mid-fight, was making just his second fight at light-heavyweight.
By the middle rounds, Parker had stayed in contention, creating difficulties for Buatsi, who operated with a protective stance to edge the better rounds.
The spectators' acceptance decreased because of constant clinching, with Parker slipping to the canvas multiple occasions during clinches.
The underdog ended stronger, but multiple periods were challenging to assess. Nevertheless, former world champion the boxing analyst - working with Dazn - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Memorial Fuels Local Rivalry Fight
In the secondary fight, Arthur beat Rea by close verdict in a excellent all-Manchester battle to secure the European light heavyweight title.
The stadium grew hushed for a extremely emotional memorial prior to the bout as 10 bells rang in remembrance of the city's native Ricky Hatton, who died 46 years old in September.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the concluding sound ended, the stillness transitioned to a roar of "there's just one Hatton".
The action inside the ropes matched the emotion. The eventual winner was floored by a left hook directly to the face in the second round, standing uncertainly to his feet on the eight count.
But the traditional red shorts of Arthur soon came forward again. Across the ring, the opponent - in competitive blue - was damaged early, significant bruising forming under his eye as the fighters traded punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the pace rarely dropped over 12 rounds.
The victor barely secured the result with scoring tallies of 114-114, close margin and 115-112, but the two athletes were relentless and courageous, all the qualities their inspiration Hatton embodied.
