UK light-heavyweight Joshua Buatsi made a winning yet unimpressive debut to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a close ten-round fight at the boxing arena.
But Parker found success, connecting with powerful single shots in a contest where the techniques didn't complement each other, with constant grabbing spoiling the contest.
Two judges scored it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my best display but how do champions respond? They succeed," the victor stated in the ring as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Some ringside observers thought the challenger, thirty-one, merited the victory but the contender experienced the second setback of his 28-fight career.
The Champion Secures Triumph in Slow Encounter
The fighter's advancement has stalled in recent years through management issues and extended periods of lack of fights.
Earlier forecast as the future of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what seems like a ultimate opportunity - under fresh management.
He started carefully, with neither fighter prepared to take risks in a tentative initial rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in 2022 after damaging his hand mid-fight, was competing in only his second fight at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who utilized a tight guard to edge the more effective rounds.
The crowd's patience wore thin because of regular grabbing, with Parker falling to the floor several times during close exchanges.
Parker finished the stronger, but many rounds were difficult to score. However, former world champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor advances, but with the caliber of heavy hitter David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Motivates All-Manchester Battle
In the co-main event, Lyndon Arthur beat Rea by split-decision in a outstanding local rivalry battle to secure the European light-heavyweight title.
The stadium fell silent for a extremely emotional memorial ahead of the contest as ten bells sounded in memory of Manchester's own Hatton, who died at age 46 in last month.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the concluding sound ended, the quiet transitioned to a roar of "there's just one Ricky Hatton".
The competition during the bout matched the emotion. Arthur was knocked down by a powerful punch squarely on the jaw in the initial stage, standing uncertainly to his footing on the referee's count.
But the red-colored shorts of the fighter soon advanced again. On the opposite side, the opponent - in rival City blue - was injured quickly, significant bruising forming under his face as the fighters exchanged punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with stinging uppercuts as the pace seldom decreased over 12 rounds.
The victor narrowly won the result with judges scorecards of even score, narrow lead and wider gap, but the two athletes were relentless and brave, exactly what their hero the legend embodied.
