UK light-heavyweight Joshua Buatsi secured a victory yet disappointing start to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a close 10-round fight at the boxing arena.
But Parker landed significant shots, landing some telling clean blows in a fight where the styles didn't complement each other, with frequent clinching disrupting the contest.
The officials judged it 96-94 in favor to the winner, with the third a 95-95 draw.
"It wasn't my best performance but what do champions do? They succeed," the victor commented in the ringside as he was greeted with negative reactions from the spectators.
The British fighter got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to earn a 20th career victory.
Several boxing experts thought the challenger, thirty-one, merited the win but the British boxer experienced the second loss of his 28-fight career.
Buatsi Secures Triumph in Slow Encounter
The fighter's advancement has stalled in recent times through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with both competitors willing to overcommit in a cagey early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second fight at the higher weight class.
By the halfway stage, the underdog had made it competitive, making life awkward for Buatsi, who worked behind a solid defense to edge the more effective rounds.
The spectators' acceptance decreased during regular grabbing, with Parker going down various instances during clinches.
The underdog ended stronger, but many rounds were challenging to assess. Although, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
The victor progresses, but with the presence of power puncher David Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Tribute Inspires Manchester Derby Battle
In the supporting bout, Arthur overcame Bradley Rea by close verdict in a outstanding Manchester vs Manchester contest to capture the European light-heavyweight belt.
The stadium grew hushed for a extremely emotional tribute ahead of the contest as ten bells tolled in remembrance of Manchester's own Ricky Hatton, who succumbed aged 46 in September.
It was the premier televised boxing event in the city since Hatton's death. As the final chime ended, the silence became a chant of "there's only one Hatton".
The action during the bout matched the feeling. The eventual winner was sent to the canvas by a powerful punch directly to the chin in the early round, getting up unsteadily to his feet on the referee's count.
But the Manchester United-red shorts of Arthur soon advanced again. From the other corner, Rea - in rival City blue - was marked up early, noticeable damage forming under his orbital area as the fighters traded punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the intensity seldom decreased over twelve rounds.
The victor edged the result with judges scorecards of even score, 115-113 and wider gap, but both fighters were determined and brave, exactly what their hero Hatton embodied.
