UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming start to his career under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a majority decision in a tight ten-round contest at the boxing arena.
But the challenger landed significant shots, connecting with powerful single shots in a fight where the approaches didn't complement each other, with excessive holding disrupting the action.
The officials had it 96-94 for to the winner, with the final judge a even score.
"It wasn't my best showing but what do champions do? They prevail," Buatsi stated in the arena as he was faced negative reactions from the crowd.
The Londoner got back to winning after his maiden career setback - an epic battle with his previous opponent in February - to secure a twentieth professional win.
Several boxing experts felt the challenger, thirty-one, merited the decision but the British boxer endured the second defeat of his 28-bout career.
The Champion Claims Triumph in Uneventful Match
His career development has plateaued in the past few years through management issues and extended periods of inactivity.
Earlier forecast as the rising talent of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what feels like a ultimate opportunity - under recent support.
He started carefully, with neither fighter ready to take risks in a calculated early stages.
Parker, whose only previous defeat 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 bout at light heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a tight guard to barely take the more effective periods.
The audience's tolerance decreased during frequent holding, with Parker falling to the floor multiple occasions during close exchanges.
The underdog closed well, but multiple periods were hard to judge. However, former world champion Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, awarding Buatsi just a single round.
Buatsi advances, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - on this evidence - still appears challenging.
Hatton Memorial Fuels Manchester Derby Battle
In the co-main event, Lyndon Arthur defeated Rea by split-decision in a terrific local rivalry contest to secure the continental championship.
The venue fell silent for a extremely emotional homage prior to the bout as a bell ceremony tolled in remembrance of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the first major televised fight night in the city since Hatton's passing. As the last bell ended, the silence gave way to a shout of "only one Hatton".
The competition within the ring matched the emotion. The eventual winner was knocked down by a powerful punch flush on the face in the early round, standing uncertainly to his footing on the eight count.
But the traditional red shorts of Arthur soon advanced again. Across the ring, the opponent - in opposing blue - was marked up soon, significant bruising appearing under his orbital area as the pair landed hard punches.
Rea, 27, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the pace rarely dropped over 12 rounds.
The victor narrowly won the decision with judges scorecards of 114-114, 115-113 and clearer margin, but the two athletes were persistent and courageous, all the qualities their inspiration the legend embodied.
