UK light-heavyweight Joshua Buatsi earned a win yet disappointing start to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a split decision in a close ten-round fight at the Manchester venue.
But Parker had his moments, landing some telling single shots in a contest where the approaches didn't complement each other, with excessive holding marring the fight.
The officials judged it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my finest display but how do champions respond? They prevail," Buatsi said in the arena as he was greeted with disapproval from the audience.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Various analysts believed the challenger, thirty-one, merited the win but the contender experienced the second setback of his 28-bout professional journey.
The Champion Secures Victory in Slow Match
The fighter's advancement has plateaued in recent years through contract problems and considerable time of inactivity.
Previously predicted as the next star of the British fight scene, he now finds himself trying to achieve expectations - possibly in what seems like a final roll of the dice - under recent support.
He began cautiously, with neither fighter ready to overcommit in a calculated opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in two years ago after breaking his hand in the contest, was making just his second fight at the higher weight class.
By the middle rounds, the underdog had kept it close, causing problems for the favorite, who utilized a tight guard to barely take the more effective periods.
The spectators' acceptance diminished because of regular grabbing, with Parker falling to the floor multiple occasions during grappling.
The underdog ended stronger, but many rounds were difficult to score. However, former world champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, giving Buatsi just only one stanza.
The victor advances, but with the caliber 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 Memorial Fuels Manchester Derby Contest
In the co-main event, Arthur defeated Bradley Rea by divided decision in a excellent Manchester vs Manchester fight to secure the European light heavyweight belt.
The venue grew hushed for a extremely emotional homage before the fight as 10 bells rang in honor of Manchester's own Ricky Hatton, who passed away aged 46 in September.
It was the first major televised match card in the urban center since Hatton's death. As the final chime faded, the silence became a roar of "only one Hatton".
The fighting inside the ropes equaled the emotion. The eventual winner was knocked down by a left hook directly to the chin in the second round, rising shakily to his feet on the count of eight.
But the traditional red shorts of Arthur soon advanced again. From the other corner, the opponent - in competitive blue - was injured early, heavy swelling developing under his orbital area as the pair landed hard punches.
Rea, 27, landed power punches but the champion, 34, fought fire with fire with effective uppercuts as the action rarely dropped over 12 rounds.
The victor edged the decision with judges scorecards of even score, close margin and clearer margin, but both fighters were determined and full of heart, everything their hero Hatton represented.
