UK light heavyweight Joshua Buatsi secured a victory yet unimpressive beginning to life under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a majority decision in a close 10-round bout at the Co-op Live Arena.
But the challenger had his moments, landing some telling clean blows in a fight where the styles never quite clicked, with excessive holding disrupting the fight.
The scoring judges scored it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest showing but how do champions respond? They succeed," Buatsi commented in the ring as he was met by negative reactions from the audience.
The Londoner bounced back after his maiden career setback - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Some ringside observers felt the challenger, 31, deserved the victory but the contender experienced the second defeat of his 28-match professional journey.
The Champion Earns Triumph in Dull Affair
His career development has plateaued in the past few years through management issues and long spells of inactivity.
Once tipped as the future of the British fight scene, he now stands trying to achieve expectations - perhaps in what feels like a ultimate opportunity - under fresh management.
He started carefully, with the two boxers ready to take risks in a tentative early stages.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was competing in only his second appearance at the higher weight class.
By the halfway stage, the underdog had made it competitive, causing problems for Buatsi, who worked behind a tight guard to barely take the more effective periods.
The audience's tolerance diminished amid constant clinching, with Parker slipping to the canvas several times during close exchanges.
The underdog closed well, but several stanzas were challenging to assess. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, giving Buatsi just only one stanza.
Buatsi progresses, but with the likes of hard hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Hatton Homage Inspires All-Manchester Battle
In the co-main event, Arthur beat Rea by split-decision in a excellent Manchester vs Manchester battle to capture the European light-heavyweight belt.
The stadium grew hushed for a profoundly moving memorial before the fight as 10 bells tolled in memory of local hero Ricky Hatton, who died at age 46 in recently.
It was the premier televised match card in the location since the passing of Hatton. As the last bell ended, the stillness became a roar of "only one Ricky Hatton".
The action inside the ropes reflected the sentiment. Arthur was knocked down by a left hook directly to the face in the initial stage, standing uncertainly to his position on the referee's count.
But the traditional red attire of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was injured quickly, noticeable damage developing under his face as the pair landed hard punches.
The challenger, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with powerful upward punches as the action hardly diminished over twelve rounds.
The victor barely secured the result with scoring tallies of draw, close margin and wider gap, but the two athletes were determined and full of heart, everything their hero the legend stood for.
