UK light-heavyweight Joshua Buatsi earned a win yet underwhelming start to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a tight 10-round fight at the boxing arena.
But the challenger landed significant shots, delivering effective single shots in a match where the techniques failed to mesh, with constant grabbing marring the contest.
The officials scored it 96-94 to Buatsi, with the third a even score.
"It wasn't my best showing but what defines champions? They prevail," Buatsi commented in the ring as he was greeted with boos from the audience.
The Londoner returned to winning ways after his maiden career setback - an epic battle with his previous opponent in February - to earn a 20th pro success.
Several boxing experts thought Parker, thirty-one, should have been awarded the victory but the contender suffered the second setback of his 28-match professional journey.
The Champion Claims Triumph in Uneventful Encounter
Buatsi's progress has slowed in recent times through contract problems and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to realize his potential - perhaps in what appears to be a last chance - under fresh management.
He started carefully, with the two boxers ready to take risks in a calculated opening few rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in 2022 after breaking his hand mid-fight, was competing in only his second fight at the higher weight class.
By the halfway stage, Parker had stayed in contention, creating difficulties for Buatsi, who utilized a tight guard to edge the more effective rounds.
The crowd's patience diminished amid constant clinching, with the challenger going down multiple occasions during grappling.
The underdog ended stronger, but multiple periods were difficult to score. Although, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian champion Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Hatton Memorial Inspires Local Rivalry Battle
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding local rivalry battle to capture the European light heavyweight championship.
The venue became quiet for a profoundly moving homage prior to the bout as ten bells tolled in memory of local hero Hatton, who succumbed 46 years old in September.
It was the premier televised match card in the city since Hatton's passing. As the concluding sound faded, the quiet gave way to a roar of "there's only one Ricky Hatton".
The fighting inside the ropes matched the emotion. Arthur was knocked down by a left hook squarely on the chin in the initial stage, getting up unsteadily to his feet on the referee's count.
But the Manchester United-red shorts of the fighter soon pressed ahead again. Across the ring, Rea - in rival City blue - was injured soon, heavy swelling developing under his eye as the pair landed hard punches.
Rea, twenty-seven, connected with strong blows but the champion, 34, fought fire with fire with powerful upward punches as the intensity rarely dropped over twelve rounds.
Arthur edged the verdict with official scores of draw, narrow lead and clearer margin, but both fighters were relentless and courageous, everything their idol the legend represented.
