UK light-heavyweight Joshua Buatsi earned a win yet unimpressive start to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a split decision in a competitive ten-round bout at the Co-op Live Arena.
But the challenger found success, delivering effective individual punches in a fight where the styles failed to mesh, with constant grabbing marring the action.
Two judges scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my finest performance but what defines champions? They succeed," the victor said in the ringside as he was faced negative reactions from the spectators.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in February - to earn a twentieth professional win.
Various analysts believed the challenger, thirty-one, deserved the victory but the British boxer experienced the second setback of his 28-bout professional journey.
Buatsi Secures Victory in Dull Match
The fighter's advancement has plateaued in recent years through contract problems and considerable time of inactivity.
Once tipped as the future of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors prepared to take risks in a cagey early stages.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand mid-fight, was competing in only his second bout at light heavyweight.
By the halfway stage, the underdog had stayed in contention, causing problems for the favorite, who operated with a tight guard to barely take the more effective rounds.
The crowd's patience decreased because of constant clinching, with the challenger going down multiple occasions during close exchanges.
Parker closed well, but several stanzas were challenging to assess. Nevertheless, former world champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor moves on, but with the likes of power puncher David Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
Hatton Memorial Inspires Local Rivalry Fight
In the supporting bout, Arthur beat Rea by split-decision in a excellent all-Manchester contest to capture the continental title.
The stadium became quiet for a profoundly moving tribute ahead of the contest as ten bells rang in memory of Manchester's own Hatton, who passed away 46 years old in last month.
It was the first major televised boxing event in the urban center since Hatton's death. As the final chime ended, the quiet transitioned to a roar of "there's just one Hatton".
The fighting inside the ropes reflected the sentiment. Arthur was floored by a left hook flush on the jaw in the initial stage, standing uncertainly to his feet on the count of eight.
But the red-colored equipment of the fighter soon came forward again. Across the ring, the opponent - in competitive blue - was damaged early, noticeable damage forming under his orbital area as the pair landed punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with stinging uppercuts as the action hardly diminished over the full distance.
The victor narrowly won the decision with scoring tallies of even score, 115-113 and wider gap, but the two athletes were determined and courageous, exactly what their inspiration the legend embodied.
