British light heavyweight Joshua Buatsi secured a victory yet unimpressive start to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a tight ten-round bout at the Manchester venue.
But Parker landed significant shots, connecting with powerful individual punches in a match where the styles failed to mesh, with excessive holding marring the fight.
Two judges had it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best display but what do champions do? They succeed," the victor stated in the ring as he was met by boos from the audience.
The Londoner got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a 20th pro success.
Various analysts felt the challenger, thirty-one, deserved the decision but the contender experienced the second defeat of his 28-bout professional journey.
The Champion Claims Win in Slow Match
Buatsi's progress has plateaued in recent times through contract problems and long spells of lack of fights.
Once tipped as the future of British boxing, he now is positioned trying to realize his potential - maybe in what appears to be a final roll of the dice - under fresh management.
He opened tentatively, with both competitors ready to take risks in a calculated early stages.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was participating in his second appearance at light-heavyweight.
By the middle rounds, Parker had kept it close, causing problems for the favorite, who utilized a solid defense to barely take the more effective rounds.
The crowd's patience wore thin because of frequent holding, with Parker falling to the floor multiple occasions during close exchanges.
The underdog closed well, but multiple periods were challenging to assess. However, previous titleholder the boxing analyst - commentating on Dazn - had it significantly in favor for Parker, scoring for Buatsi just one round.
The victor advances, but with the likes of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Tribute Inspires Manchester Derby Contest
In the supporting bout, Arthur overcame Bradley Rea by divided decision in a terrific Manchester vs Manchester fight to capture the continental championship.
The venue became quiet for a extremely emotional tribute prior to the bout as a bell ceremony tolled in remembrance of the city's native Ricky Hatton, who succumbed at age 46 in recently.
It was the premier televised boxing event in the city since Hatton's death. As the final chime faded, the silence transitioned to a roar of "there's only one Ricky Hatton".
The fighting during the bout equaled the feeling. The eventual winner was sent to the canvas by a left hook squarely on the chin in the second round, standing uncertainly to his feet on the count of eight.
But the red-colored attire of the fighter soon advanced again. From the other corner, the opponent - in rival City blue - was damaged early, significant bruising forming under his orbital area as the fighters landed hard punches.
Rea, 27, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the action hardly diminished over the full distance.
Arthur narrowly won the result with judges scorecards of 114-114, narrow lead and clearer margin, but each competitor were persistent and brave, everything their idol Hatton embodied.
