UK light heavyweight Joshua Buatsi secured a victory yet underwhelming debut to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a majority decision in a close ten-round fight at the Co-op Live Arena.
But the challenger found success, delivering effective clean blows in a contest where the styles never quite clicked, with constant grabbing disrupting the action.
The scoring judges scored it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my best display but how do champions respond? They prevail," Buatsi said in the ring as he was faced negative reactions from the crowd.
The Londoner bounced back after his first professional defeat - an epic battle with Callum Smith in February - to earn a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, merited the win but the contender endured the second setback of his 28-fight career.
The Champion Claims Triumph in Dull Encounter
Buatsi's progress has slowed in recent times through management issues and extended periods of lack of fights.
Previously predicted as the next star of UK boxing, he now stands trying to fulfil that early promise - maybe in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter willing to overcommit in a calculated opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after damaging his hand in the contest, was participating in his second fight at the higher weight class.
By the halfway stage, Parker had made it competitive, causing problems for Buatsi, who operated with a solid defense to barely take the cleaner rounds.
The spectators' acceptance diminished during frequent holding, with Parker going down several times during close exchanges.
The underdog ended stronger, but multiple periods were difficult to score. Nevertheless, former world champion Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
The victor advances, but with the caliber of heavy hitter David Benavidez, and Russian champion Bivol ruling the division, the journey to titles - based on this performance - still looks steep.
Hatton Memorial Motivates Manchester Derby Contest
In the secondary fight, Arthur defeated Rea by split-decision in a excellent local rivalry contest to capture the European light heavyweight title.
The stadium fell silent for a deeply poignant homage ahead of the contest as a bell ceremony sounded in honor of local hero Hatton, who died aged 46 in September.
It was the first major televised match card in the location since Hatton's passing. As the concluding sound ended, the silence became a shout of "only one Hatton".
The action inside the ropes reflected the feeling. The eventual winner was floored by a left hook flush on the face in the early round, getting up unsteadily to his position on the referee's count.
But the red-colored attire of Arthur soon came forward again. Across the ring, the opponent - in competitive blue - was marked up early, heavy swelling appearing under his eye as the pair traded powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with stinging uppercuts as the pace seldom decreased over twelve rounds.
The victor narrowly won the decision with judges scorecards of 114-114, close margin and clearer margin, but both fighters were persistent and full of heart, everything their hero Hatton embodied.
