UK light-heavyweight Joshua Buatsi earned a win yet unimpressive beginning to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a majority decision in a competitive 10-round bout at the boxing arena.
But the challenger had his moments, landing some telling single shots in a fight where the techniques never quite clicked, with constant grabbing marring the fight.
Two 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," Buatsi said in the ring as he was met by disapproval from the audience.
The Londoner bounced back after his maiden career setback - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Some ringside observers felt the challenger, thirty-one, deserved the win but the Derbyshire fighter endured the second setback of his 28-match career.
The Champion Claims Win in Slow Affair
The fighter's advancement has slowed in the past few years through promotional disputes and extended periods of inactivity.
Previously predicted as the future of UK boxing, he now is positioned trying to fulfil that early promise - maybe in what seems like a final roll of the dice - under fresh management.
He started carefully, with both competitors willing to be aggressive in a tentative opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after damaging his hand in the contest, was making just his second bout at the higher weight class.
By the fight's midpoint, Parker had made it competitive, making life awkward for Buatsi, who worked behind a solid defense to barely take the better rounds.
The crowd's patience diminished during regular grabbing, with Parker slipping to the canvas various instances during clinches.
The underdog closed well, but several stanzas were hard to judge. Although, former world champion Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, giving Buatsi just a single round.
The victor progresses, but with the likes of heavy hitter David Benavidez, and Russian star Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Hatton Memorial Fuels Manchester Derby Contest
In the supporting bout, Lyndon Arthur beat Rea by close verdict in a terrific Manchester vs Manchester battle to secure the European light-heavyweight title.
The stadium became quiet for a deeply poignant memorial ahead of the contest as ten bells tolled in remembrance of the city's native Ricky Hatton, who died 46 years old in last month.
It was the premier televised boxing event in the location since Hatton's death. As the concluding sound disappeared, the quiet gave way to a shout of "only one Ricky Hatton".
The fighting during the bout equaled the feeling. Arthur was floored by a significant blow flush on the jaw in the second round, rising shakily to his position on the referee's count.
But the Manchester United-red equipment of Arthur soon came forward again. From the other corner, Rea - in opposing blue - was damaged early, noticeable damage developing under his face as the pair landed punishing blows.
Rea, 27, landed power punches but the champion, 34, fought fire with fire with stinging uppercuts as the pace seldom decreased over 12 rounds.
The victor narrowly won the result with judges scorecards of draw, narrow lead and wider gap, but the two athletes were relentless and courageous, everything their inspiration the legend stood for.
