UK light-heavyweight Joshua Buatsi earned a win yet disappointing start to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a tight ten-round fight at the Manchester venue.
But Parker found success, connecting with powerful individual punches in a match where the approaches never quite clicked, with frequent clinching spoiling the action.
The officials scored it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my greatest display but how do champions respond? They succeed," the victor commented in the ringside as he was met by boos from the crowd.
The British fighter bounced back after his maiden career setback - an epic battle with his previous opponent in last winter - to claim a twentieth professional win.
Several boxing experts felt the challenger, thirty-one, deserved the victory but the contender suffered the second setback of his 28-match professional journey.
Buatsi Earns Victory in Uneventful Encounter
Buatsi's progress has slowed in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the rising talent of the British fight scene, he now finds himself trying to realize his potential - maybe in what appears to be a final roll of the dice - under fresh management.
He started carefully, with neither fighter ready to overcommit in a cagey early stages.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after damaging his hand mid-fight, was competing in only his second bout at light heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a solid defense to edge the better periods.
The spectators' acceptance diminished during frequent holding, with the challenger going down various instances during close exchanges.
The underdog finished the stronger, but multiple periods were hard to judge. However, former world champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
Buatsi moves on, but with the presence of power puncher David Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Hatton Tribute Fuels All-Manchester Battle
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a outstanding local rivalry fight to capture the continental title.
The venue fell silent for a deeply poignant homage before the fight as a bell ceremony rang in remembrance of local hero Ricky Hatton, who succumbed 46 years old in last month.
It was the first major televised boxing event in the location since Hatton's death. As the last bell disappeared, the quiet transitioned to a shout of "there's only one Ricky Hatton".
The competition within the ring matched the feeling. The eventual winner was floored by a left hook squarely on the jaw in the initial stage, standing uncertainly to his footing on the eight count.
But the traditional red attire of the fighter soon advanced again. Across the ring, the opponent - in rival City blue - was marked up quickly, significant bruising developing under his eye as the pair traded powerful shots.
Rea, 27, connected with strong blows but Arthur, 34, fought fire with fire with effective uppercuts as the action seldom decreased over twelve rounds.
Arthur edged the result with scoring tallies of even score, narrow lead and wider gap, but both fighters were persistent and brave, exactly what their hero Hatton stood for.
