British light heavyweight Joshua Buatsi earned a win yet unimpressive start to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive ten-round bout at the boxing arena.
But Parker found success, connecting with powerful clean blows in a match where the styles didn't complement each other, with frequent clinching marring the action.
The scoring judges had it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my finest performance but what defines champions? They win," the victor commented in the ring as he was greeted with negative reactions from the crowd.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to earn a 20th pro success.
Various analysts believed the challenger, thirty-one, deserved the victory but the contender endured the second loss of his 28-bout professional journey.
The Champion Earns Triumph in Slow Match
Buatsi's progress has plateaued in recent years through promotional disputes and considerable time of lack of fights.
Earlier forecast as the next star of British boxing, he now stands trying to fulfil that early promise - maybe in what feels like a last chance - under fresh management.
He opened tentatively, with the two boxers ready to take risks in a calculated initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after damaging his hand during the bout, was participating in his second fight at light-heavyweight.
By the middle rounds, Parker had stayed in contention, making life awkward for Buatsi, who operated with a protective stance to edge the more effective periods.
The spectators' acceptance diminished amid constant clinching, with the challenger falling to the floor several times during close exchanges.
Parker closed well, but several stanzas were challenging to assess. Nevertheless, previous titleholder Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
The victor progresses, but with the caliber of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - judging by this showing - still appears challenging.
Hatton Memorial Fuels Local Rivalry Fight
In the co-main event, Arthur defeated Bradley Rea by split-decision in a terrific Manchester vs Manchester battle to win the continental championship.
The stadium fell silent for a profoundly moving tribute ahead of the contest as a bell ceremony tolled in remembrance of the city's native Hatton, who succumbed aged 46 in September.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the final chime disappeared, the silence became a roar of "only one Hatton".
The competition within the ring equaled the sentiment. The eventual winner was floored by a powerful punch directly to the face in the initial stage, getting up unsteadily to his footing on the eight count.
But the red-colored equipment of Arthur soon pressed ahead again. Across the ring, Rea - in opposing blue - was injured early, heavy swelling forming under his orbital area as the duo traded punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with stinging uppercuts as the pace seldom decreased over 12 rounds.
The victor edged the decision with official scores of even score, narrow lead and 115-112, but the two athletes were relentless and courageous, exactly what their hero Hatton represented.
