UK light heavyweight Joshua Buatsi earned a win yet underwhelming start to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a split decision in a close ten-round contest at the Co-op Live Arena.
But the challenger found success, delivering effective clean blows in a fight where the techniques failed to mesh, with constant grabbing spoiling the action.
The scoring judges judged it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my best display but what defines champions? They win," the victor stated in the ringside as he was met by boos from the crowd.
The British fighter returned to winning ways after his maiden career setback - an epic battle with Callum Smith in February - to earn a 20th pro success.
Several boxing experts felt Parker, 31, merited the victory but the British boxer endured the second defeat of his 28-match professional journey.
The Champion Earns Victory in Uneventful Affair
Buatsi's progress has stalled in the past few years through management issues and extended periods of inactivity.
Once tipped as the rising talent of UK boxing, he now stands trying to realize his potential - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with the two boxers ready to take risks in a calculated opening few rounds.
Parker, 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 fight at light heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for the favorite, who utilized a solid defense to barely take the more effective stanzas.
The spectators' acceptance decreased during frequent holding, with Parker going down multiple occasions during clinches.
Parker closed well, but many rounds were difficult to score. Nevertheless, ex-champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, giving Buatsi just a single round.
Buatsi moves on, but with the presence of heavy hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Hatton Homage Motivates Local Rivalry Battle
In the co-main event, Arthur overcame Rea by divided decision in a excellent local rivalry battle to win the European light heavyweight belt.
The stadium fell silent for a profoundly moving homage before the fight as ten bells tolled in honor of local hero Ricky Hatton, who died 46 years old in September.
It was the first major televised boxing event in the urban center since the passing of Hatton. As the concluding sound disappeared, the stillness gave way to a chant of "only one Ricky Hatton".
The fighting within the ring equaled the sentiment. The eventual winner was sent to the canvas by a left hook flush on the chin in the second round, standing uncertainly to his feet on the count of eight.
But the traditional red shorts of the fighter soon came forward again. From the other corner, Rea - in opposing blue - was injured soon, noticeable damage appearing under his eye as the duo exchanged punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with stinging uppercuts as the action rarely dropped over 12 rounds.
The victor narrowly won the verdict with scoring tallies of 114-114, close margin and clearer margin, but each competitor were persistent and full of heart, exactly what their inspiration the legend embodied.
