UK light-heavyweight Joshua Buatsi secured a victory yet disappointing start to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a close 10-round bout at the Co-op Live Arena.
But Parker found success, landing some telling clean blows in a match where the techniques failed to mesh, with constant grabbing marring the action.
Two judges scored it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest display but what do champions do? They win," the victor stated in the ring as he was greeted with boos from the spectators.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to earn a 20th pro success.
Several boxing experts felt the challenger, 31, deserved the decision but the contender experienced the second defeat of his 28-bout career.
The Champion Earns Victory in Dull Affair
His career development has slowed in recent times through management issues and extended periods of inactivity.
Earlier forecast as the rising talent of UK boxing, he now stands trying to realize his potential - possibly in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with neither fighter prepared to be aggressive in a cagey opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after suffering a hand injury in the contest, was making just his second bout at light-heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for the favorite, who utilized a tight guard to narrowly win the more effective periods.
The spectators' acceptance decreased amid constant clinching, with the challenger falling to the floor various instances during close exchanges.
The underdog closed well, but multiple periods were difficult to score. Nevertheless, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just one round.
The victor advances, but with the caliber of hard hitter David Benavidez, and Russian star Bivol leading the category, the path to championship success - judging by this showing - still seems difficult.
Hatton Memorial Fuels Local Rivalry Contest
In the co-main event, Arthur defeated Bradley Rea by close verdict in a outstanding Manchester vs Manchester contest to capture the continental belt.
The arena fell silent for a deeply poignant tribute prior to the bout as ten bells rang in remembrance of Manchester's own Ricky Hatton, who succumbed 46 years old in September.
It was the first major televised fight night in the city since Hatton's passing. As the last bell disappeared, the silence became a roar of "there's only one Ricky Hatton".
The action during the bout equaled the sentiment. The eventual winner was knocked down by a powerful punch directly to the chin in the initial stage, getting up unsteadily to his position on the eight count.
But the Manchester United-red shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was marked up early, noticeable damage forming under his face as the duo landed punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with stinging uppercuts as the intensity rarely dropped over 12 rounds.
Arthur narrowly won the result with judges scorecards of 114-114, close margin and wider gap, but each competitor were relentless and full of heart, everything their hero the legend represented.
