UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming debut to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a tight 10-round fight at the boxing arena.
But the challenger had his moments, delivering effective single shots in a fight where the approaches didn't complement each other, with excessive holding marring the action.
The scoring judges judged it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my best display but how do champions respond? They win," the victor stated in the arena as he was met by disapproval from the spectators.
The British fighter got back to winning after his initial pro loss - an memorable fight with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, merited the victory but the British boxer experienced the second setback of his 28-match career.
The Champion Secures Win in Dull Affair
The fighter's advancement has plateaued in the past few years through management issues and extended periods of inactivity.
Earlier forecast as the rising talent of UK boxing, he now finds himself trying to achieve expectations - possibly in what feels like a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter willing to overcommit in a cagey initial rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after damaging his hand in the contest, was competing in only his second appearance at the higher weight class.
By the halfway stage, Parker had kept it close, making life awkward for the favorite, who operated with a protective stance to edge the more effective stanzas.
The audience's tolerance decreased because of frequent holding, with Parker slipping to the canvas various instances during close exchanges.
The underdog finished the stronger, but multiple periods were challenging to assess. However, former world champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
The victor advances, but with the caliber of power puncher David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Homage Motivates All-Manchester Battle
In the co-main event, Lyndon Arthur defeated Rea by divided decision in a outstanding Manchester vs Manchester fight to win the European light-heavyweight championship.
The stadium became quiet for a deeply poignant tribute before the fight as 10 bells sounded in honor of local hero Ricky Hatton, who died 46 years old in September.
It was the premier televised fight night in the city since Hatton's passing. As the final chime faded, the quiet gave way to a roar of "there's just one Ricky Hatton".
The action within the ring matched the feeling. Arthur was floored by a left hook directly to the jaw in the second round, standing uncertainly to his position on the referee's count.
But the traditional red equipment of the fighter soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was injured soon, significant bruising forming under his orbital area as the duo landed hard punches.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace hardly diminished over 12 rounds.
The victor barely secured the result with judges scorecards of 114-114, 115-113 and wider gap, but each competitor were relentless and brave, all the qualities their idol Hatton stood for.
