UK light heavyweight Joshua Buatsi earned a win yet unimpressive start to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a split decision in a tight 10-round fight at the Manchester venue.
But the challenger found success, landing some telling individual punches in a contest where the approaches failed to mesh, with excessive holding marring the fight.
The officials scored it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my best showing but what do champions do? They win," the victor said in the ring as he was faced negative reactions from the crowd.
The British fighter got back to winning after his maiden career setback - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Various analysts felt the challenger, 31, should have been awarded the win but the contender experienced the second setback of his 28-fight professional journey.
The Champion Earns Triumph in Uneventful Encounter
His career development has plateaued in recent times through management issues and considerable time of lack of fights.
Previously predicted as the next star of British boxing, he now is positioned trying to achieve expectations - perhaps in what appears to be a last chance - under recent support.
He began cautiously, with the two boxers willing to overcommit in a calculated early stages.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand in the contest, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for the favorite, who worked behind a tight guard to barely take the cleaner stanzas.
The spectators' acceptance wore thin during regular grabbing, with the challenger going down various instances during close exchanges.
The underdog closed well, but multiple periods were hard to judge. Nevertheless, former world champion the boxing analyst - working with Dazn - had it particularly wide for the challenger, giving Buatsi just a single round.
Buatsi moves on, but with the presence of heavy hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - on this evidence - still looks steep.
Hatton Memorial Motivates Manchester Derby Fight
In the co-main event, Arthur defeated Bradley Rea by divided decision in a excellent all-Manchester fight to capture the European light-heavyweight championship.
The stadium grew hushed for a deeply poignant homage before the fight as a bell ceremony sounded in memory of the city's native Ricky Hatton, who passed away 46 years old in recently.
It was the premier televised match card in the location since Hatton's passing. As the last bell ended, the silence transitioned to a roar of "there's just one Hatton".
The competition during the bout equaled the emotion. Arthur was sent to the canvas by a left hook directly to the chin in the early round, standing uncertainly to his position on the eight count.
But the traditional red equipment of Arthur soon came forward again. Across the ring, the opponent - in competitive blue - was marked up early, significant bruising appearing under his orbital area as the duo landed powerful shots.
The challenger, 27, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the intensity rarely dropped over twelve rounds.
The victor barely secured the verdict with scoring tallies of draw, close margin and 115-112, but the two athletes were persistent and courageous, all the qualities their idol the legend embodied.
