British light heavyweight Joshua Buatsi secured a victory yet unimpressive debut to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a split decision in a tight 10-round fight at the boxing arena.
But Parker found success, delivering effective individual punches in a match where the styles failed to mesh, with excessive holding disrupting the action.
Two judges judged it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my best display but what defines champions? They succeed," the victor stated in the arena as he was faced negative reactions from the crowd.
The British fighter got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Various analysts felt the challenger, 31, merited the decision but the contender endured the second loss of his 28-fight professional journey.
Buatsi Secures Victory in Slow Match
Buatsi's progress has plateaued in recent years through management issues and considerable time of inactivity.
Once tipped as the future of the British fight scene, he now is positioned trying to realize his potential - perhaps in what feels like a last chance - under new promotional backing.
He opened tentatively, with both competitors prepared to be aggressive in a tentative early stages.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after damaging his hand during the bout, was participating in his second bout at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who utilized a protective stance to edge the more effective periods.
The audience's tolerance diminished amid constant clinching, with the challenger slipping to the canvas various instances during close exchanges.
Parker closed well, but many rounds were challenging to assess. Although, former world champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
The victor moves on, but with the likes of heavy hitter Benavidez, and Russian star Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Hatton Homage Motivates Manchester Derby Contest
In the supporting bout, Arthur defeated Rea by close verdict in a excellent all-Manchester battle to secure the European light heavyweight championship.
The arena became quiet for a profoundly moving tribute before the fight as 10 bells rang in remembrance of local hero Hatton, who succumbed at age 46 in September.
It was the first major televised fight night in the urban center since Hatton's death. As the last bell disappeared, the stillness transitioned to a shout of "only one Ricky Hatton".
The action during the bout matched the feeling. The eventual winner was sent to the canvas by a left hook squarely on the face in the early round, standing uncertainly to his footing on the count of eight.
But the red-colored shorts of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was marked up soon, significant bruising appearing under his eye as the fighters landed powerful shots.
The challenger, 27, landed power punches but the champion, 34, responded in kind with effective uppercuts as the action rarely dropped over the full distance.
Arthur narrowly won the verdict with scoring tallies of draw, close margin and 115-112, but the two athletes were persistent and courageous, everything their idol Hatton embodied.
