British light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a split decision in a tight 10-round contest at the Manchester venue.
But the challenger landed significant shots, landing some telling individual punches in a fight where the techniques never quite clicked, with excessive holding disrupting the action.
Two judges scored it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest performance but how do champions respond? They prevail," Buatsi said in the ring as he was faced negative reactions from the audience.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th pro success.
Some ringside observers believed Parker, 31, deserved the decision but the British boxer experienced the second setback of his 28-bout career.
The Champion Earns Triumph in Uneventful Encounter
His career development has plateaued in recent years through promotional disputes and considerable time of inactivity.
Once tipped as the next star of UK boxing, he now stands trying to fulfil that early promise - possibly in what feels like a last chance - under fresh management.
He began cautiously, with neither fighter willing to overcommit in a tentative early stages.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was making just his second fight at the higher weight class.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who utilized a protective stance to edge the cleaner periods.
The audience's tolerance diminished amid regular grabbing, with Parker going down various instances during close exchanges.
Parker closed well, but many rounds were difficult to score. Although, ex-champion the boxing analyst - working with the broadcast network - had it particularly wide for Parker, giving Buatsi just one round.
The victor advances, but with the likes of hard hitter Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Homage Fuels Local Rivalry Battle
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a excellent all-Manchester fight to secure the European light heavyweight title.
The stadium became quiet for a deeply poignant homage prior to the bout as 10 bells tolled in honor of Manchester's own Ricky Hatton, who passed away 46 years old in recently.
It was the initial significant broadcast match card in the location since Hatton's passing. As the last bell ended, the stillness became a chant of "there's just one Ricky Hatton".
The action within the ring reflected the emotion. The eventual winner was floored by a left hook squarely on the jaw in the early round, standing uncertainly to his feet on the count of eight.
But the Manchester United-red equipment of the fighter soon pressed ahead again. From the other corner, the opponent - in competitive blue - was damaged soon, heavy swelling developing under his face as the duo landed hard punches.
The challenger, 27, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the action hardly diminished over twelve rounds.
Arthur narrowly won the result with official scores of even score, 115-113 and clearer margin, but both fighters were persistent and courageous, all the qualities their hero the legend stood for.
