UK light heavyweight Joshua Buatsi earned a win yet underwhelming debut to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a competitive ten-round bout at the Manchester venue.
But Parker had his moments, delivering effective single shots in a fight where the techniques failed to mesh, with constant grabbing disrupting the fight.
The scoring judges had it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my best performance but what do champions do? They succeed," Buatsi stated in the arena as he was greeted with disapproval from the spectators.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in February - to claim a twentieth professional win.
Several boxing experts felt Parker, 31, should have been awarded the victory but the Derbyshire fighter endured the second setback of his 28-fight career.
Buatsi Secures Triumph in Slow Match
His career development has plateaued in recent times through management issues and long spells of inactivity.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - maybe in what feels like a last chance - under recent support.
He started carefully, with neither fighter ready to take risks in a calculated initial rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after suffering a hand injury during the bout, was participating in his second bout at the higher weight class.
By the fight's midpoint, Parker had kept it close, creating difficulties for the favorite, who utilized a protective stance to barely take the better stanzas.
The audience's tolerance wore thin during constant clinching, with Parker going down several times during close exchanges.
Parker ended stronger, but many rounds were challenging to assess. Nevertheless, former world champion the boxing analyst - commentating on Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Memorial Inspires Manchester Derby Battle
In the co-main event, Arthur overcame Rea by split-decision in a excellent local rivalry contest to capture the European light-heavyweight title.
The arena became quiet for a deeply poignant memorial prior to the bout as a bell ceremony tolled in honor of the city's native Ricky Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the last bell disappeared, the stillness gave way to a roar of "only one Hatton".
The competition inside the ropes reflected the sentiment. Arthur was floored by a powerful punch squarely on the chin in the initial stage, rising shakily to his position on the eight count.
But the red-colored attire of Arthur soon advanced again. On the opposite side, Rea - in competitive blue - was marked up quickly, noticeable damage forming under his eye as the pair exchanged powerful shots.
The challenger, twenty-seven, landed power punches but the champion, 34, matched the intensity with powerful upward punches as the action rarely dropped over 12 rounds.
Arthur narrowly won the decision with official scores of 114-114, close margin and 115-112, but both fighters were persistent and brave, all the qualities their inspiration Hatton stood for.
