British light heavyweight Joshua Buatsi made a winning yet unimpressive start to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a majority decision in a competitive 10-round contest at the Manchester venue.
But the challenger had his moments, landing some telling clean blows in a fight where the techniques never quite clicked, with excessive holding spoiling the contest.
Two judges scored it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my greatest showing but how do champions respond? They succeed," the victor said in the ringside as he was faced negative reactions from the crowd.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in February - to claim a twentieth professional win.
Some ringside observers felt the challenger, 31, merited the win but the Derbyshire fighter suffered the second defeat of his 28-fight career.
The Champion Earns Win in Slow Encounter
The fighter's advancement has slowed in recent years through contract problems and long spells of lack of fights.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors prepared to overcommit in a tentative opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was participating in his second fight at light-heavyweight.
By the middle rounds, Parker had kept it close, causing problems for the favorite, who worked behind a tight guard to narrowly win the better rounds.
The crowd's patience decreased during frequent holding, with the challenger slipping to the canvas various instances during clinches.
The underdog closed well, but many rounds were challenging to assess. Nevertheless, previous titleholder Carl Frampton - working with Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
Buatsi moves on, but with the caliber of power puncher David Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - on this evidence - still seems difficult.
Hatton Homage Inspires Local Rivalry Contest
In the co-main event, Lyndon Arthur overcame Rea by split-decision in a excellent all-Manchester battle to secure the continental title.
The stadium fell silent for a profoundly moving tribute before the fight as a bell ceremony rang in remembrance of the city's native Hatton, who succumbed 46 years old in recently.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the final chime faded, the quiet transitioned to a chant of "there's only one Ricky Hatton".
The action during the bout matched the emotion. Arthur was knocked down by a left hook directly to the chin in the second round, rising shakily to his position on the eight count.
But the traditional red attire of Arthur soon came forward again. Across the ring, Rea - in competitive blue - was damaged soon, noticeable damage developing under his face as the pair traded punishing blows.
Rea, 27, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace rarely dropped over 12 rounds.
Arthur narrowly won the result with judges scorecards of draw, 115-113 and wider gap, but both fighters were determined and brave, exactly what their hero Hatton stood for.
