British light heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a split decision in a close ten-round fight at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful individual punches in a contest where the styles failed to mesh, with constant grabbing spoiling the contest.
The officials judged it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my greatest showing but what do champions do? They prevail," the victor commented in the ring as he was met by negative reactions from the crowd.
The British fighter bounced back after his first professional defeat - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Several boxing experts thought the challenger, 31, deserved the win but the British boxer experienced the second defeat of his 28-fight professional journey.
The Champion Earns Triumph in Uneventful Encounter
His career development has stalled in recent times through promotional disputes and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now is positioned trying to realize his potential - perhaps in what appears to be a ultimate opportunity - under recent support.
He started carefully, with the two boxers prepared to overcommit in a cagey opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was competing in only his second fight at the higher weight class.
By the halfway stage, Parker had kept it close, causing problems for Buatsi, who worked behind a solid defense to barely take the better rounds.
The audience's tolerance decreased because of regular grabbing, with the challenger going down several times during grappling.
The underdog ended stronger, but many rounds were difficult to score. Nevertheless, previous titleholder Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just one round.
The victor advances, but with the likes of heavy hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Tribute Fuels All-Manchester Fight
In the co-main event, Arthur beat Rea by close verdict in a excellent all-Manchester battle to win the European light-heavyweight belt.
The venue fell silent for a deeply poignant tribute before the fight as a bell ceremony sounded in memory of Manchester's own Hatton, who succumbed 46 years old in recently.
It was the initial significant broadcast match card in the urban center since the passing of Hatton. As the concluding sound disappeared, the silence gave way to a chant of "only one Hatton".
The action during the bout matched the emotion. Arthur was knocked down by a powerful punch directly to the chin in the initial stage, rising shakily to his feet on the count of eight.
But the Manchester United-red shorts of the fighter soon pressed ahead again. Across the ring, Rea - in rival City blue - was injured early, significant bruising developing under his face as the pair traded hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace seldom decreased over 12 rounds.
Arthur barely secured the decision with official scores of draw, narrow lead and 115-112, but both fighters were determined and brave, all the qualities their hero the legend represented.
