UK light-heavyweight Joshua Buatsi earned a win yet disappointing beginning to his career under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a tight ten-round bout at the Co-op Live Arena.
But Parker landed significant shots, landing some telling single shots in a fight where the styles failed to mesh, with excessive holding marring the action.
The officials judged it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my greatest showing but how do champions respond? They succeed," Buatsi stated in the ring as he was greeted with disapproval from the spectators.
The British fighter bounced back after his initial pro loss - an thrilling contest with his previous opponent in February - to claim a twentieth professional win.
Various analysts felt the challenger, thirty-one, should have been awarded the victory but the contender endured the second defeat of his 28-bout professional journey.
Buatsi Claims Victory in Dull Affair
Buatsi's progress has plateaued in recent times through management issues and considerable time of lack of fights.
Once tipped as the next star of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with neither fighter willing to take risks in a tentative initial rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was making just his second appearance at the higher weight class.
By the fight's midpoint, the underdog had kept it close, creating difficulties for Buatsi, who operated with a protective stance to edge the cleaner rounds.
The spectators' acceptance diminished during frequent holding, with the challenger going down various instances during grappling.
Parker ended stronger, but multiple periods were challenging to assess. Although, former world champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
The victor advances, but with the presence of power puncher David Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - based on this performance - still looks steep.
Hatton Tribute Fuels All-Manchester Fight
In the supporting bout, Lyndon Arthur defeated Bradley Rea by divided decision in a terrific all-Manchester fight to win the continental belt.
The stadium grew hushed for a deeply poignant homage prior to the bout as 10 bells rang in memory of Manchester's own Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the concluding sound faded, the quiet gave way to a roar of "there's just one Hatton".
The action within the ring reflected the sentiment. Arthur was knocked down by a powerful punch flush on the jaw in the second round, getting up unsteadily to his footing on the referee's count.
But the Manchester United-red shorts of the fighter soon pressed ahead again. Across the ring, the opponent - in competitive blue - was marked up soon, heavy swelling developing under his orbital area as the pair landed hard punches.
The challenger, twenty-seven, landed power punches but the champion, 34, matched the intensity with stinging uppercuts as the pace hardly diminished over the full distance.
Arthur edged the decision with judges scorecards of draw, narrow lead and clearer margin, but the two athletes were persistent and brave, exactly what their hero Hatton embodied.
