UK light heavyweight Joshua Buatsi made a winning yet unimpressive beginning 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 fight at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling single shots in a contest where the styles never quite clicked, with frequent clinching spoiling the fight.
The scoring judges had it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my finest showing but what do champions do? They succeed," the victor said in the arena as he was met by negative reactions from the spectators.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers believed the challenger, 31, deserved the win but the Derbyshire fighter experienced the second defeat of his 28-bout career.
The Champion Earns Victory in Uneventful Match
His career development has plateaued in recent years through management issues and considerable time of lack of fights.
Once tipped as the next star of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a last chance - under new promotional backing.
He opened tentatively, with neither fighter willing to take risks in a cagey early stages.
The challenger, whose sole prior loss came at super middleweight against John Ryder in 2022 after damaging his hand mid-fight, was participating in his second bout at the higher weight class.
By the halfway stage, Parker had made it competitive, causing problems for Buatsi, who operated with a protective stance to barely take the better periods.
The spectators' acceptance decreased during regular grabbing, with the challenger falling to the floor multiple occasions during close exchanges.
Parker ended stronger, but many rounds were challenging to assess. Although, previous titleholder the boxing analyst - commentating on Dazn - had it significantly in favor for Parker, scoring for Buatsi just one round.
The victor moves on, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Tribute Fuels All-Manchester Contest
In the co-main event, Arthur beat Bradley Rea by divided decision in a excellent all-Manchester contest to win the European light-heavyweight belt.
The venue became quiet for a profoundly moving memorial ahead of the contest as a bell ceremony sounded in remembrance of Manchester's own Hatton, who passed away 46 years old in September.
It was the premier televised match card in the city since Hatton's passing. As the last bell faded, the silence became a roar of "there's only one Ricky Hatton".
The action within the ring equaled the emotion. Arthur was knocked down by a left hook squarely on the jaw in the early round, rising shakily to his position on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. From the other corner, Rea - in opposing blue - was marked up soon, noticeable damage forming under his face as the pair traded hard punches.
Rea, 27, connected with strong blows but the champion, thirty-four, responded in kind with powerful upward punches as the action seldom decreased over twelve rounds.
The victor barely secured the decision with scoring tallies of even score, close margin and clearer margin, but both fighters were persistent and courageous, exactly what their inspiration Hatton embodied.
