UK light-heavyweight Joshua Buatsi earned a win yet unimpressive start to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a split decision in a tight 10-round contest at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a contest where the approaches didn't complement each other, with excessive holding disrupting the contest.
The scoring judges had it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my greatest performance but how do champions respond? They win," the victor stated in the ring as he was faced disapproval from the crowd.
The Londoner bounced back after his initial pro loss - an epic battle with his previous opponent in February - to claim a 20th pro success.
Several boxing experts thought the challenger, thirty-one, should have been awarded the victory but the British boxer experienced the second defeat of his 28-bout career.
The Champion Secures Win in Slow Encounter
His career development has stalled in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of the British fight scene, he now stands trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under recent support.
He started carefully, with both competitors prepared to overcommit in a calculated early stages.
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 competing in only his second bout at light-heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for Buatsi, who utilized a tight guard to narrowly win the better stanzas.
The audience's tolerance decreased amid regular grabbing, with the challenger going down various instances during close exchanges.
The underdog finished the stronger, but multiple periods were hard to judge. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor progresses, but with the presence of power puncher David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Hatton Homage Fuels Manchester Derby Contest
In the co-main event, Arthur defeated Bradley Rea by split-decision in a excellent local rivalry contest to secure the European light-heavyweight title.
The arena grew hushed for a profoundly moving homage prior to the bout as ten bells rang in memory of the city's native Hatton, who died aged 46 in last month.
It was the initial significant broadcast fight night in the city since Hatton's death. As the last bell disappeared, the quiet gave way to a roar of "there's only one Ricky Hatton".
The action during the bout reflected the feeling. Arthur was sent to the canvas by a significant blow squarely on the jaw in the initial stage, getting up unsteadily to his feet on the eight count.
But the Manchester United-red shorts of the fighter soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was injured early, significant bruising developing under his face as the fighters traded hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action hardly diminished over the full distance.
Arthur narrowly won the result with scoring tallies of draw, narrow lead and clearer margin, but the two athletes were persistent and full of heart, all the qualities their hero Hatton represented.
