UK light-heavyweight Joshua Buatsi secured a victory yet disappointing debut to life under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a majority decision in a tight ten-round bout at the boxing arena.
But Parker found success, delivering effective clean blows in a contest where the techniques failed to mesh, with frequent clinching marring the action.
The officials judged it 96-94 to the winner, with the third a 95-95.
"It wasn't my finest display but how do champions respond? They win," Buatsi stated in the arena as he was greeted with negative reactions from the crowd.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in last winter - to secure a twentieth professional win.
Several boxing experts thought Parker, thirty-one, should have been awarded the win but the Derbyshire fighter endured the second defeat of his 28-fight career.
The Champion Claims Triumph in Uneventful Encounter
Buatsi's progress has plateaued in recent times through promotional disputes and extended periods of lack of fights.
Previously predicted as the rising talent of British boxing, he now stands trying to achieve expectations - possibly in what feels like a ultimate opportunity - under fresh management.
He opened tentatively, with the two boxers willing to take risks in a tentative opening few rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was participating in his second bout at light heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a protective stance to narrowly win the better rounds.
The spectators' acceptance decreased because of frequent holding, with the challenger falling to the floor several times during grappling.
The underdog closed well, but multiple periods were hard to judge. However, ex-champion the boxing analyst - working with Dazn - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
Buatsi advances, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - on this evidence - still appears challenging.
Hatton Homage Inspires Manchester Derby Contest
In the supporting bout, Arthur beat Bradley Rea by split-decision in a excellent Manchester vs Manchester contest to capture the European light heavyweight championship.
The stadium fell silent for a extremely emotional memorial prior to the bout as a bell ceremony tolled in honor of the city's native Ricky Hatton, who died at age 46 in recently.
It was the initial significant broadcast match card in the city since Hatton's death. As the concluding sound faded, the quiet became a chant of "there's only one Hatton".
The competition during the bout reflected the sentiment. The eventual winner was knocked down by a left hook directly to the jaw in the initial stage, standing uncertainly to his footing on the eight count.
But the red-colored equipment of the fighter soon pressed ahead again. From the other corner, the opponent - in opposing blue - was damaged early, heavy swelling appearing under his orbital area as the fighters exchanged punishing blows.
The challenger, 27, connected with strong blows but Arthur, 34, matched the intensity with stinging uppercuts as the pace rarely dropped over the full distance.
Arthur barely secured the result with scoring tallies of draw, narrow lead and 115-112, but each competitor were determined and courageous, everything their inspiration Hatton represented.
