UK light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to life under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a competitive ten-round contest at the boxing arena.
But the challenger had his moments, delivering effective single shots in a contest where the techniques never quite clicked, with frequent clinching disrupting the fight.
Two judges judged it 96-94 for to the winner, with the third a even score.
"It wasn't my best performance but what defines champions? They win," the victor stated in the arena as he was faced disapproval from the crowd.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in last winter - to earn a twentieth professional win.
Several boxing experts believed Parker, 31, merited the win but the contender experienced the second setback of his 28-fight professional journey.
Buatsi Secures Triumph in Dull Affair
Buatsi's progress has slowed in recent years through management issues and long spells of inactivity.
Earlier forecast as the future of British boxing, he now stands trying to realize his potential - maybe in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors prepared to take risks in a cagey initial rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after breaking his hand during the bout, was making just his second bout at the higher weight class.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who operated with a tight guard to narrowly win the better rounds.
The spectators' acceptance decreased because of frequent holding, with Parker falling to the floor multiple occasions during close exchanges.
Parker finished the stronger, but many rounds were challenging to assess. Nevertheless, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, giving Buatsi just only one stanza.
The victor progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - based on this performance - still appears challenging.
Ricky Hatton Homage Fuels Manchester Derby Fight
In the co-main event, Arthur defeated Rea by divided decision in a excellent local rivalry battle to secure the European light-heavyweight belt.
The venue grew hushed for a profoundly moving memorial prior to the bout as 10 bells rang in remembrance of local hero Hatton, who died 46 years old in recently.
It was the initial significant broadcast boxing event in the urban center since the passing of Hatton. As the last bell ended, the silence gave way to a chant of "there's only one Hatton".
The action during the bout matched the feeling. The eventual winner was knocked down by a significant blow directly to the jaw in the second round, standing uncertainly to his footing on the referee's count.
But the red-colored shorts of the fighter soon advanced again. Across the ring, Rea - in opposing blue - was marked up quickly, heavy swelling forming under his face as the pair landed hard punches.
The challenger, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with effective uppercuts as the intensity hardly diminished over twelve rounds.
The victor narrowly won the verdict with official scores of 114-114, 115-113 and clearer margin, but both fighters were relentless and courageous, everything their idol Hatton stood for.
