UK light heavyweight Joshua Buatsi earned a win yet unimpressive start to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a competitive ten-round fight at the boxing arena.
But the challenger found success, connecting with powerful single shots in a fight where the styles never quite clicked, with frequent clinching spoiling the contest.
The officials scored it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my finest performance but what do champions do? They win," the victor stated in the ring as he was greeted with negative reactions from the spectators.
The British fighter returned to winning ways after his initial pro loss - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Various analysts felt the challenger, 31, should have been awarded the decision but the Derbyshire fighter endured the second setback of his 28-match professional journey.
The Champion Secures Win in Slow Match
Buatsi's progress has slowed in the past few years through contract problems and extended periods of inactivity.
Earlier forecast as the rising talent of British boxing, he now is positioned trying to realize his potential - possibly in what feels like a ultimate opportunity - under recent support.
He began cautiously, with both competitors willing to overcommit in a calculated opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in 2022 after breaking his hand in the contest, was participating in his second appearance at light-heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for the favorite, who operated with a tight guard to narrowly win the cleaner rounds.
The crowd's patience decreased during regular grabbing, with Parker going down several times during grappling.
The underdog closed well, but several stanzas were difficult to score. Although, former world champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, giving Buatsi just a single round.
The victor progresses, but with the presence of power puncher David Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - judging by this showing - still seems difficult.
Hatton Homage Motivates All-Manchester Battle
In the secondary fight, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding local rivalry contest to capture the European light-heavyweight belt.
The arena fell silent for a deeply poignant memorial prior to the bout as a bell ceremony sounded in remembrance of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised match card in the city since the passing of Hatton. As the last bell ended, the stillness transitioned to a shout of "there's just one Ricky Hatton".
The action during the bout matched the emotion. The eventual winner was knocked down by a significant blow squarely on the face in the early round, rising shakily to his footing on the count of eight.
But the Manchester United-red equipment of Arthur soon pressed ahead again. Across the ring, the opponent - in opposing blue - was damaged early, noticeable damage forming under his orbital area as the duo traded hard punches.
Rea, 27, landed power punches but the champion, thirty-four, matched the intensity with stinging uppercuts as the pace rarely dropped over twelve rounds.
The victor barely secured the result with judges scorecards of draw, narrow lead and wider gap, but both fighters were persistent and full of heart, everything their idol Hatton stood for.
