British light heavyweight Joshua Buatsi earned a win yet underwhelming start to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a majority decision in a tight ten-round contest at the boxing arena.
But the challenger found success, delivering effective clean blows in a fight where the approaches failed to mesh, with frequent clinching marring the action.
The officials judged it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest display but how do champions respond? They win," Buatsi stated in the ringside as he was met by boos from the crowd.
The Londoner bounced back after his maiden career setback - an thrilling contest with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers felt the challenger, 31, merited the win but the contender experienced the second loss of his 28-match career.
Buatsi Earns Triumph in Slow Encounter
The fighter's advancement has plateaued in recent times through promotional disputes and considerable time of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now is positioned trying to realize his potential - maybe in what feels like a final roll of the dice - under fresh management.
He started carefully, with both competitors willing to be aggressive in a cagey early stages.
Parker, whose only previous defeat came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was competing in only his second appearance at the higher weight class.
By the middle rounds, the underdog had stayed in contention, causing problems for Buatsi, who operated with a solid defense to edge the cleaner periods.
The spectators' acceptance wore thin because of frequent holding, with the challenger falling to the floor various instances during clinches.
Parker finished the stronger, but several stanzas were hard to judge. Nevertheless, former world champion Carl Frampton - working with Dazn - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor advances, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Hatton Tribute Inspires All-Manchester Fight
In the supporting bout, Arthur defeated Rea by close verdict in a outstanding Manchester vs Manchester fight to capture the European light heavyweight championship.
The venue fell silent for a profoundly moving tribute prior to the bout as a bell ceremony sounded in honor of local hero Ricky Hatton, who passed away aged 46 in September.
It was the first major televised match card in the location since the passing of Hatton. As the concluding sound ended, the silence became a shout of "there's just one Ricky Hatton".
The competition within the ring equaled the sentiment. The eventual winner was knocked down by a significant blow squarely on the face in the second round, getting up unsteadily to his footing on the referee's count.
But the red-colored attire of Arthur soon pressed ahead again. Across the ring, the opponent - in opposing blue - was injured soon, significant bruising developing under his face as the pair exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with stinging uppercuts as the pace seldom decreased over 12 rounds.
The victor barely secured the decision with scoring tallies of 114-114, 115-113 and 115-112, but both fighters were persistent and brave, everything their inspiration the legend stood for.
