British light heavyweight Joshua Buatsi secured a victory yet unimpressive beginning to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a close 10-round contest at the boxing arena.
But Parker found success, connecting with powerful individual punches in a match where the styles didn't complement each other, with constant grabbing disrupting the contest.
The officials had it 96-94 to Buatsi, with the final judge a 95-95.
"It wasn't my best display but what defines champions? They succeed," the victor commented in the ring as he was greeted with negative reactions from the audience.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in February - to claim a 20th career victory.
Several boxing experts thought the challenger, thirty-one, should have been awarded the decision but the contender endured the second loss of his 28-match professional journey.
Buatsi Earns Triumph in Dull Affair
The fighter's advancement has plateaued in recent years through promotional disputes and long spells of inactivity.
Previously predicted as the rising talent of UK boxing, he now finds himself trying to realize his potential - perhaps in what appears to be a ultimate opportunity - under recent support.
He started carefully, with the two boxers willing to take risks in a calculated initial rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after suffering a hand injury mid-fight, was making just his second fight at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to edge the cleaner rounds.
The crowd's patience decreased because of frequent holding, with Parker falling to the floor various instances during close exchanges.
The underdog closed well, but many rounds were difficult to score. Although, ex-champion Carl Frampton - commentating on Dazn - had it strongly leaning for Parker, scoring for Buatsi just one round.
The victor advances, but with the caliber of hard hitter David Benavidez, and Russian champion Bivol leading the category, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Homage Fuels Manchester Derby Battle
In the supporting bout, Lyndon Arthur beat Bradley Rea by divided decision in a excellent local rivalry contest to win the European light heavyweight belt.
The arena fell silent for a extremely emotional tribute prior to the bout as 10 bells rang in memory of the city's native Ricky Hatton, who succumbed 46 years old in last month.
It was the first major televised boxing event in the urban center since the passing of Hatton. As the concluding sound ended, the silence transitioned to a shout of "there's just one Hatton".
The fighting within the ring reflected the sentiment. Arthur was knocked down by a powerful punch directly to the chin in the second round, rising shakily to his position on the referee's count.
But the red-colored equipment of the fighter soon pressed ahead again. From the other corner, the opponent - in opposing blue - was marked up soon, noticeable damage developing under his orbital area as the fighters traded hard punches.
Rea, 27, connected with strong blows but Arthur, thirty-four, fought fire with fire with effective uppercuts as the action seldom decreased over the full distance.
The victor barely secured the result with official scores of draw, close margin and 115-112, but the two athletes were persistent and courageous, exactly what their inspiration the legend embodied.
