UK light-heavyweight Joshua Buatsi earned a win yet underwhelming start to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a split decision in a tight 10-round bout at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful clean blows in a match where the approaches failed to mesh, with constant grabbing spoiling the contest.
Two judges scored it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest display but what do champions do? They win," the victor commented in the arena as he was met by disapproval from the spectators.
The British fighter got back to winning after his first professional defeat - an epic battle with Callum Smith in last winter - to earn a 20th career victory.
Various analysts thought the challenger, thirty-one, should have been awarded the win but the contender suffered the second setback of his 28-fight career.
The Champion Claims Triumph in Uneventful Match
Buatsi's progress has stalled in the past few years through management issues and long spells of inactivity.
Earlier forecast as the next star of UK boxing, he now stands trying to fulfil that early promise - perhaps in what seems like a last chance - under fresh management.
He began cautiously, with neither fighter ready 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 during the bout, was competing in only his second bout at the higher weight class.
By the fight's midpoint, Parker had made it competitive, creating difficulties for Buatsi, who utilized a protective stance to narrowly win the more effective periods.
The spectators' acceptance decreased amid frequent holding, with the challenger falling to the floor several times during close exchanges.
The underdog ended stronger, but several stanzas were hard to judge. Nevertheless, ex-champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the likes of heavy hitter Benavidez, and Russian star Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Memorial Inspires Manchester Derby Battle
In the co-main event, Lyndon Arthur defeated Bradley Rea by close verdict in a excellent all-Manchester contest to secure the European light heavyweight title.
The venue grew hushed for a deeply poignant homage ahead of the contest as a bell ceremony rang in honor of Manchester's own Hatton, who passed away aged 46 in September.
It was the premier televised match card in the city since Hatton's death. As the concluding sound ended, the quiet became a chant of "only one Hatton".
The competition during the bout reflected the sentiment. The eventual winner was floored by a significant blow flush on the jaw in the initial stage, getting up unsteadily to his position on the eight count.
But the red-colored equipment of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was damaged soon, heavy swelling developing under his face as the pair exchanged punishing blows.
Rea, 27, delivered effective strikes but the champion, 34, responded in kind with stinging uppercuts as the pace hardly diminished over twelve rounds.
Arthur barely secured the result with official scores of even score, 115-113 and clearer margin, but both fighters were determined and brave, everything their idol the legend represented.
