UK light-heavyweight Joshua Buatsi earned a win yet underwhelming debut to life under new promoters with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a majority decision in a close ten-round bout at the boxing arena.
But the challenger landed significant shots, connecting with powerful clean blows in a contest where the styles didn't complement each other, with constant grabbing spoiling the action.
The scoring judges had it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my best showing but what do champions do? They succeed," the victor commented in the ringside as he was greeted with boos from the spectators.
The Londoner got back to winning after his maiden career setback - an epic battle with his previous opponent in last winter - to claim a 20th career victory.
Several boxing experts believed Parker, 31, merited the decision but the contender suffered the second setback of his 28-fight professional journey.
The Champion Claims Win in Uneventful Encounter
His career development has plateaued in recent times through promotional disputes and considerable time of inactivity.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what feels like a ultimate opportunity - under fresh management.
He opened tentatively, with the two boxers prepared to be aggressive in a cagey initial rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in 2022 after damaging his hand in the contest, was participating in his second appearance at light-heavyweight.
By the middle rounds, Parker had kept it close, creating difficulties for the favorite, who worked behind a solid defense to narrowly win the more effective stanzas.
The audience's tolerance diminished because of regular grabbing, with the challenger falling to the floor multiple occasions during close exchanges.
The underdog ended stronger, but many rounds were difficult to score. Although, ex-champion Carl Frampton - working with the broadcast network - had it particularly wide for Parker, giving Buatsi just a single round.
The victor 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 looks steep.
Ricky Hatton Homage Inspires Manchester Derby Contest
In the secondary fight, Arthur beat Bradley Rea by divided decision in a terrific Manchester vs Manchester fight to capture the European light-heavyweight belt.
The arena became quiet for a extremely emotional homage prior to the bout as ten bells rang in honor of the city's native Hatton, who died 46 years old in recently.
It was the initial significant broadcast match card in the city since Hatton's death. As the final chime ended, the quiet gave way to a roar of "there's only one Ricky Hatton".
The competition during the bout reflected the feeling. The eventual winner was floored by a significant blow directly to the face in the early round, rising shakily to his feet on the eight count.
But the traditional red equipment of Arthur soon advanced again. From the other corner, the opponent - in competitive blue - was damaged quickly, noticeable damage forming under his face as the pair traded powerful shots.
Rea, 27, landed power punches but Arthur, thirty-four, fought fire with fire with powerful upward punches as the pace seldom decreased over 12 rounds.
The victor narrowly won the verdict with scoring tallies of 114-114, 115-113 and clearer margin, but the two athletes were determined and full of heart, everything their inspiration the legend embodied.
