British light-heavyweight Joshua Buatsi made a winning yet underwhelming start to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a split decision in a tight 10-round contest at the Co-op Live Arena.
But the challenger found success, delivering effective clean blows in a match where the approaches never quite clicked, with constant grabbing disrupting the fight.
Two judges had it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest display but how do champions respond? They win," Buatsi said in the ringside as he was met by negative reactions from the spectators.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in February - to earn a 20th career victory.
Some ringside observers believed the challenger, 31, merited the decision but the contender endured the second setback of his 28-match professional journey.
The Champion Earns Win in Uneventful Encounter
His career development has slowed in recent years through contract problems and considerable time of inactivity.
Once tipped as the next star of UK boxing, he now is positioned trying to fulfil that early promise - perhaps in what seems like a last chance - under fresh management.
He started carefully, with both competitors ready to overcommit in a calculated opening few rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was participating in his second fight at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for Buatsi, who operated with a solid defense to narrowly win the cleaner stanzas.
The spectators' acceptance decreased amid frequent holding, with Parker slipping to the canvas several times during grappling.
Parker ended stronger, but multiple periods were hard to judge. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just one round.
Buatsi advances, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Hatton Homage Fuels All-Manchester Contest
In the secondary fight, Arthur defeated Rea by divided decision in a outstanding all-Manchester fight to win the continental belt.
The arena grew hushed for a profoundly moving homage before the fight as a bell ceremony rang in honor of the city's native Ricky Hatton, who died 46 years old in September.
It was the premier televised boxing event in the urban center since Hatton's death. As the final chime disappeared, the stillness transitioned to a roar of "there's just one Hatton".
The action inside the ropes reflected the feeling. Arthur was sent to the canvas by a left hook flush on the jaw in the early round, getting up unsteadily to his footing on the referee's count.
But the red-colored equipment of Arthur soon advanced again. From the other corner, Rea - in rival City blue - was marked up early, heavy swelling forming under his orbital area as the pair landed hard punches.
The challenger, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with effective uppercuts as the pace rarely dropped over twelve rounds.
The victor narrowly won the result with judges scorecards of draw, 115-113 and wider gap, but both fighters were relentless and courageous, all the qualities their hero Hatton stood for.
