UK light heavyweight Joshua Buatsi made a winning yet disappointing beginning to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a judges' verdict in a competitive ten-round contest at the Manchester venue.
But the challenger had his moments, connecting with powerful individual punches in a contest where the approaches never quite clicked, with constant grabbing spoiling the action.
The officials scored it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my finest display but what do champions do? They prevail," the victor said in the arena as he was faced boos from the spectators.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th career victory.
Some ringside observers believed Parker, thirty-one, deserved the decision but the British boxer experienced the second defeat of his 28-fight career.
The Champion Secures Win in Uneventful Match
The fighter's advancement has plateaued in recent years through contract problems and considerable time of inactivity.
Earlier forecast as the rising talent of British boxing, he now finds himself trying to achieve expectations - perhaps in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with neither fighter ready to be aggressive in a calculated opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after damaging his hand in the contest, was participating in his second appearance at the higher weight class.
By the middle rounds, Parker had made it competitive, creating difficulties for Buatsi, who utilized a protective stance to barely take the cleaner periods.
The audience's tolerance decreased amid frequent holding, with the challenger falling to the floor several times during grappling.
Parker finished the stronger, but multiple periods were challenging to assess. Although, ex-champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for Parker, giving Buatsi just only one stanza.
The victor progresses, but with the likes of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Memorial Motivates Local Rivalry Fight
In the supporting bout, Arthur overcame Bradley Rea by divided decision in a outstanding local rivalry fight to capture the European light heavyweight belt.
The stadium grew hushed for a extremely emotional tribute ahead of the contest as ten bells sounded in honor of the city's native Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised match card in the city since the passing of Hatton. As the final chime disappeared, the quiet gave way to a chant of "there's just one Hatton".
The fighting during the bout reflected the feeling. Arthur was sent to the canvas by a significant blow squarely on the chin in the initial stage, rising shakily to his position on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. Across the ring, Rea - in opposing blue - was marked up early, noticeable damage forming under his eye as the duo landed punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with stinging uppercuts as the action hardly diminished over twelve rounds.
The victor barely secured the verdict with scoring tallies of 114-114, close margin and 115-112, but both fighters were relentless and full of heart, all the qualities their inspiration Hatton stood for.
