British light heavyweight Joshua Buatsi earned a win yet unimpressive debut to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's work rate likely gained him a split decision in a tight 10-round bout at the boxing arena.
But Parker found success, connecting with powerful individual punches in a contest where the approaches never quite clicked, with excessive holding marring the action.
Two judges scored it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my finest display but what do champions do? They win," the victor stated in the arena as he was greeted with boos from the spectators.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Several boxing experts believed the challenger, thirty-one, merited the victory but the contender endured the second defeat of his 28-match professional journey.
Buatsi Claims Victory in Uneventful Encounter
His career development has slowed in the past few years through contract problems and long spells of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a last chance - under fresh management.
He started carefully, with both competitors willing to be aggressive in a calculated early stages.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was competing in only his second appearance at the higher weight class.
By the halfway stage, Parker had stayed in contention, creating difficulties for the favorite, who operated with a solid defense to narrowly win the better periods.
The audience's tolerance decreased amid constant clinching, with Parker going down various instances during clinches.
The underdog finished the stronger, but multiple periods were hard to judge. Although, ex-champion Carl Frampton - commentating on Dazn - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor advances, but with the likes of power puncher David Benavidez, and Russian star Bivol ruling the division, the road to world glory - based on this performance - still appears challenging.
Hatton Homage Motivates Local Rivalry Fight
In the supporting bout, Lyndon Arthur overcame Bradley Rea by split-decision in a outstanding local rivalry contest to capture the continental championship.
The venue fell silent for a deeply poignant memorial before the fight as ten bells tolled in remembrance of Manchester's own Hatton, who succumbed 46 years old in September.
It was the first major televised match card in the location since Hatton's death. As the final chime ended, the stillness transitioned to a roar of "only one Ricky Hatton".
The action inside the ropes reflected the emotion. The eventual winner was sent to the canvas by a powerful punch squarely on the face in the initial stage, rising shakily to his position on the count of eight.
But the traditional red equipment of the fighter soon came forward again. Across the ring, the opponent - in opposing blue - was marked up soon, significant bruising forming under his eye as the fighters traded powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with stinging uppercuts as the pace hardly diminished over 12 rounds.
The victor barely secured the verdict with official scores of draw, 115-113 and wider gap, but the two athletes were relentless and brave, everything their idol the legend represented.
