UK light-heavyweight Joshua Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a competitive 10-round bout at the Manchester venue.
But the challenger had his moments, landing some telling individual punches in a contest where the approaches failed to mesh, with excessive holding spoiling the action.
The officials scored it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best showing but what defines champions? They prevail," the victor stated in the ringside as he was met by boos from the spectators.
The British fighter bounced back after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Some ringside observers believed Parker, 31, should have been awarded the win but the contender experienced the second defeat of his 28-bout professional journey.
Buatsi Secures Victory in Slow Affair
The fighter's advancement has plateaued in recent times through contract problems and long spells of lack of fights.
Once tipped as the rising talent of the British fight scene, he now stands trying to fulfil that early promise - possibly in what feels like a ultimate opportunity - under new promotional backing.
He opened tentatively, with neither fighter ready to overcommit in a calculated early stages.
The challenger, whose sole prior loss came at the lower weight class 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 fight's midpoint, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a protective stance to edge the better rounds.
The spectators' acceptance decreased amid constant clinching, with Parker slipping to the canvas multiple occasions during close exchanges.
The underdog closed well, but several stanzas were difficult to score. Nevertheless, former world champion Carl Frampton - working with Dazn - had it significantly in favor for Parker, giving Buatsi just a single round.
The victor moves on, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - on this evidence - still appears challenging.
Hatton Memorial Inspires Local Rivalry Contest
In the co-main event, Arthur defeated Rea by split-decision in a excellent all-Manchester contest to secure the continental belt.
The arena fell silent for a deeply poignant tribute prior to the bout as 10 bells rang in memory of Manchester's own Hatton, who died 46 years old in September.
It was the first major televised boxing event in the urban center since Hatton's passing. As the last bell disappeared, the silence gave way to a roar of "there's just one Hatton".
The competition within the ring equaled the emotion. The eventual winner was floored by a left hook flush on the chin in the early round, rising shakily to his position on the referee's count.
But the red-colored equipment of Arthur soon came forward again. Across the ring, the opponent - in rival City blue - was damaged early, noticeable damage forming under his orbital area as the duo traded punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the action hardly diminished over twelve rounds.
Arthur edged the verdict with official scores of draw, close margin and clearer margin, but both fighters were persistent and courageous, exactly what their idol Hatton embodied.
