British light heavyweight Joshua Buatsi made a winning yet unimpressive start to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a tight 10-round fight at the boxing arena.
But the challenger found success, delivering effective single shots in a contest where the styles never quite clicked, with excessive holding disrupting the action.
Two judges judged it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my finest showing but what defines champions? They win," Buatsi said in the arena as he was faced disapproval from the crowd.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in last winter - to claim a 20th pro success.
Some ringside observers felt the challenger, 31, merited the decision but the contender endured the second loss of his 28-match professional journey.
The Champion Claims Triumph in Dull Affair
His career development has plateaued in the past few years through contract problems and long spells of inactivity.
Once tipped as the rising talent of British boxing, he now stands trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under fresh management.
He started carefully, with neither fighter ready to overcommit in a tentative opening few rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in 2022 after breaking his hand during the bout, was participating in his second appearance at the higher weight class.
By the halfway stage, the underdog had kept it close, creating difficulties for the favorite, who operated with a protective stance to narrowly win the more effective rounds.
The crowd's patience wore thin because of regular grabbing, with Parker slipping to the canvas several times during close exchanges.
The underdog closed well, but many rounds were difficult to score. Nevertheless, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, giving Buatsi just one round.
Buatsi progresses, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - on this evidence - still looks steep.
Hatton Homage Fuels Local Rivalry Fight
In the supporting bout, Arthur beat Bradley Rea by split-decision in a terrific all-Manchester battle to secure the continental belt.
The arena fell silent for a profoundly moving tribute before the fight as 10 bells tolled in honor of local hero Ricky Hatton, who died at age 46 in September.
It was the premier televised fight night in the location since Hatton's passing. As the final chime faded, the stillness gave way to a roar of "there's only one Ricky Hatton".
The action within the ring equaled the feeling. The eventual winner was knocked down by a left hook flush on the jaw in the early round, standing uncertainly to his footing on the eight count.
But the red-colored attire of Arthur soon pressed ahead again. On the opposite side, Rea - in competitive blue - was marked up early, noticeable damage developing under his eye as the pair exchanged powerful shots.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action rarely dropped over the full distance.
Arthur barely secured the verdict with official scores of draw, close margin and 115-112, but both fighters were persistent and courageous, exactly what their inspiration the legend stood for.
