British light-heavyweight Joshua Buatsi earned a win yet unimpressive start to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a split decision in a close ten-round fight at the Manchester venue.
But Parker landed significant shots, delivering effective single shots in a fight where the techniques failed to mesh, with constant grabbing marring the action.
Two judges scored it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest performance but how do champions respond? They succeed," Buatsi said in the arena as he was met by boos from the crowd.
The Londoner bounced back after his first professional defeat - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers felt the challenger, thirty-one, deserved the decision but the contender endured the second defeat of his 28-fight career.
Buatsi Claims Triumph in Uneventful Affair
The fighter's advancement has slowed in recent years through contract problems and long spells of inactivity.
Once tipped as the rising talent of UK boxing, he now is positioned trying to realize his potential - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors prepared to take risks in a calculated initial rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after breaking his hand mid-fight, was making just his second bout at light heavyweight.
By the halfway stage, the underdog had kept it close, creating difficulties for the favorite, who operated with a tight guard to edge the better periods.
The spectators' acceptance decreased during frequent holding, with the challenger slipping to the canvas several times during grappling.
The underdog finished the stronger, but many rounds were difficult to score. Nevertheless, ex-champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, giving Buatsi just one round.
The victor progresses, but with the likes of power puncher Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Hatton Tribute Motivates Local Rivalry Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific all-Manchester battle to win the European light heavyweight belt.
The stadium grew hushed for a extremely emotional memorial before the fight as 10 bells sounded in honor of the city's native Hatton, who succumbed aged 46 in last month.
It was the first major televised match card in the location since Hatton's passing. As the last bell ended, the quiet transitioned to a chant of "there's only one Ricky Hatton".
The fighting within the ring reflected the sentiment. The eventual winner was floored by a left hook flush on the jaw in the second round, standing uncertainly to his feet on the count of eight.
But the Manchester United-red shorts of Arthur soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was damaged early, noticeable damage appearing under his face as the fighters traded hard punches.
The challenger, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with stinging uppercuts as the pace hardly diminished over twelve rounds.
Arthur edged the decision with official scores of 114-114, 115-113 and wider gap, but both fighters were persistent and courageous, all the qualities their inspiration the legend embodied.
