UK light heavyweight Joshua Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a competitive ten-round fight at the Manchester venue.
But Parker had his moments, connecting with powerful individual punches in a contest where the approaches failed to mesh, with frequent clinching spoiling the fight.
The scoring judges scored it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest performance but what defines champions? They win," Buatsi said in the ringside as he was greeted with boos from the audience.
The British fighter got back to winning after his first professional defeat - an memorable fight with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts felt Parker, thirty-one, deserved the decision but the contender suffered the second loss of his 28-fight career.
The Champion Earns Win in Uneventful Match
The fighter's advancement has slowed in recent times through management issues and extended periods of inactivity.
Once tipped as the rising talent of UK boxing, he now stands trying to fulfil that early promise - maybe in what appears to be a last chance - under new promotional backing.
He began cautiously, with both competitors ready to take risks in a calculated initial rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury in the contest, was making just his second appearance at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for Buatsi, who worked behind a tight guard to narrowly win the more effective periods.
The audience's tolerance diminished during frequent holding, with the challenger going down various instances during close exchanges.
The underdog finished the stronger, but several stanzas were challenging to assess. However, previous titleholder Carl Frampton - working with Dazn - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor progresses, but with the likes of power puncher David Benavidez, and Russian champion Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Hatton Tribute Motivates Local Rivalry Contest
In the co-main event, Arthur beat Rea by split-decision in a excellent all-Manchester battle to win the continental championship.
The venue became quiet for a extremely emotional memorial ahead of the contest as ten bells sounded in remembrance of local hero Ricky Hatton, who died 46 years old in last month.
It was the first major televised boxing event in the urban center since Hatton's death. As the concluding sound faded, the stillness gave way to a chant of "only one Ricky Hatton".
The fighting inside the ropes reflected the emotion. Arthur was knocked down by a powerful punch directly to the chin in the second round, standing uncertainly to his footing on the eight count.
But the red-colored attire of the fighter soon came forward again. On the opposite side, Rea - in competitive blue - was injured quickly, heavy swelling forming under his orbital area as the pair exchanged powerful shots.
The challenger, 27, landed power punches but the champion, thirty-four, matched the intensity with stinging uppercuts as the action seldom decreased over 12 rounds.
Arthur barely secured the verdict with judges scorecards of 114-114, close margin and 115-112, but each competitor were relentless and courageous, all the qualities their hero Hatton represented.
