British light-heavyweight Joshua Buatsi earned a win yet underwhelming beginning to his career under recent management with a decision win 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 boxing arena.
But Parker landed significant shots, landing some telling individual punches in a match where the approaches didn't complement each other, with excessive holding spoiling the action.
The officials had it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my best display but what defines champions? They win," Buatsi commented in the ringside as he was faced disapproval from the spectators.
The British fighter got back to winning after his first professional defeat - an memorable fight with his previous opponent in last winter - to secure a 20th pro success.
Various analysts thought Parker, 31, should have been awarded the win but the British boxer suffered the second defeat of his 28-match professional journey.
The Champion Earns Triumph in Dull Affair
The fighter's advancement has stalled in recent times through management issues and considerable time of inactivity.
Once tipped as the future of UK boxing, he now stands trying to fulfil that early promise - perhaps in what appears to be a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter prepared to take risks in a calculated early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after damaging his hand mid-fight, was making just his second fight at light-heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a tight guard to barely take the cleaner stanzas.
The audience's tolerance diminished during frequent holding, with Parker going down various instances during close exchanges.
Parker ended stronger, but multiple periods were difficult to score. However, former world champion the boxing analyst - working with the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor progresses, but with the presence of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Hatton Tribute Fuels Manchester Derby Contest
In the co-main event, Arthur beat Bradley Rea by divided decision in a excellent all-Manchester contest to win the continental title.
The venue became quiet for a profoundly moving tribute prior to the bout as 10 bells sounded in honor of the city's native Hatton, who succumbed at age 46 in last month.
It was the premier televised fight night in the urban center since Hatton's death. As the last bell disappeared, the quiet became a roar of "only one Hatton".
The fighting during the bout reflected the emotion. The eventual winner was floored by a significant blow squarely on the face in the second round, getting up unsteadily to his feet on the count of eight.
But the red-colored equipment of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was marked up early, heavy swelling developing under his orbital area as the pair traded powerful shots.
Rea, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with powerful upward punches as the intensity rarely dropped over twelve rounds.
The victor edged the verdict with scoring tallies of even score, close margin and clearer margin, but each competitor were relentless and full of heart, everything their inspiration the legend represented.
