UK light heavyweight Joshua Buatsi secured a victory yet underwhelming debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a split decision in a competitive 10-round bout at the Co-op Live Arena.
But the challenger found success, landing some telling individual punches in a match where the styles failed to mesh, with constant grabbing spoiling the action.
The officials scored it 96-94 for to the winner, with the final judge a 95-95.
"It wasn't my best performance but what do champions do? They succeed," Buatsi commented in the arena as he was greeted with disapproval from the crowd.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Various analysts felt Parker, thirty-one, should have been awarded the decision but the British boxer suffered the second loss of his 28-bout career.
The Champion Secures Victory in Uneventful Affair
His career development has slowed in the past few years through promotional disputes and considerable time of inactivity.
Earlier forecast as the next star of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under fresh management.
He started carefully, with the two boxers prepared to overcommit in a tentative early stages.
Parker, whose only previous defeat came at super middleweight against John Ryder in 2022 after breaking his hand during the bout, was making just his second bout at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a tight guard to edge the better rounds.
The spectators' acceptance decreased during frequent holding, with Parker falling to the floor various instances during grappling.
Parker closed well, but several stanzas were difficult to score. Although, previous titleholder Carl Frampton - working with the broadcast network - had it particularly wide for Parker, awarding Buatsi just only one stanza.
The victor advances, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Fuels Manchester Derby Fight
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding local rivalry contest to secure the European light-heavyweight championship.
The venue grew hushed for a profoundly moving memorial before the fight as 10 bells tolled in honor of the city's native Hatton, who passed away at age 46 in September.
It was the first major televised match card in the city since Hatton's passing. As the concluding sound faded, the quiet transitioned to a chant of "only one Ricky Hatton".
The action during the bout reflected the emotion. The eventual winner was floored by a left hook squarely on the face in the early round, standing uncertainly to his feet on the eight count.
But the traditional red attire of the fighter soon pressed ahead again. Across the ring, the opponent - in rival City blue - was injured early, noticeable damage appearing under his eye as the fighters traded powerful shots.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the action seldom decreased over the full distance.
The victor barely secured the verdict with judges scorecards of 114-114, narrow lead and 115-112, but each competitor were persistent and full of heart, everything their idol the legend embodied.
