British light-heavyweight Joshua Buatsi earned a win yet disappointing beginning to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a split decision in a competitive 10-round fight at the Manchester venue.
But Parker had his moments, delivering effective individual punches in a fight where the techniques failed to mesh, with excessive holding spoiling the action.
The scoring judges had it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best showing but how do champions respond? They succeed," the victor said in the arena as he was faced boos from the audience.
The Londoner bounced back after his first professional defeat - an thrilling contest with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers felt the challenger, thirty-one, should have been awarded the victory but the contender suffered the second setback of his 28-match professional journey.
The Champion Claims Victory in Slow Affair
Buatsi's progress has stalled in recent times through management issues and considerable time of inactivity.
Once tipped as the next star of UK boxing, he now finds himself trying to realize his potential - maybe in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers prepared to overcommit in a cagey initial rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was participating in his second appearance at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for the favorite, who worked behind a protective stance to edge the more effective rounds.
The audience's tolerance wore thin during constant clinching, with the challenger falling to the floor multiple occasions during close exchanges.
The underdog ended stronger, but many rounds were hard to judge. Although, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor moves on, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Memorial Inspires Manchester Derby Fight
In the supporting bout, Arthur overcame Rea by close verdict in a excellent local rivalry contest to secure the European light heavyweight championship.
The stadium grew hushed for a deeply poignant homage ahead of the contest as a bell ceremony rang in memory of Manchester's own Hatton, who succumbed at age 46 in last month.
It was the first major televised fight night in the urban center since the passing of Hatton. As the concluding sound ended, the quiet gave way to a chant of "only one Hatton".
The action within the ring matched the emotion. The eventual winner was floored by a powerful punch flush on the chin in the initial stage, rising shakily to his feet on the count of eight.
But the Manchester United-red equipment of Arthur soon advanced again. Across the ring, Rea - in opposing blue - was damaged soon, noticeable damage appearing under his face as the pair exchanged powerful shots.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, matched the intensity with stinging uppercuts as the intensity hardly diminished over twelve rounds.
The victor edged the result with official scores of 114-114, close margin and 115-112, but the two athletes were determined and brave, all the qualities their hero Hatton embodied.
