UK light heavyweight Joshua Buatsi secured a victory yet unimpressive start to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a split decision in a competitive 10-round bout at the Manchester venue.
But Parker found success, delivering effective individual punches in a fight where the approaches failed to mesh, with excessive holding marring the action.
Two judges judged it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They win," the victor stated in the ringside as he was greeted with boos from the crowd.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a twentieth professional win.
Some ringside observers thought the challenger, 31, should have been awarded the decision but the Derbyshire fighter experienced the second setback of his 28-bout career.
Buatsi Secures Triumph in Slow Match
The fighter's advancement has slowed in recent years through contract problems and considerable time of inactivity.
Once tipped as the rising talent of British boxing, he now finds himself trying to realize his potential - perhaps in what feels like a last chance - under fresh management.
He began cautiously, with both competitors prepared to take risks in a tentative opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second fight at light-heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for Buatsi, who worked behind a protective stance to edge the more effective rounds.
The crowd's patience decreased during constant clinching, with the challenger going down various instances during clinches.
Parker finished the stronger, but multiple periods were difficult to score. Nevertheless, former world champion the boxing analyst - working with the broadcast network - had it particularly wide for Parker, awarding Buatsi just one round.
Buatsi advances, but with the likes of hard hitter David Benavidez, and Russian star Bivol leading the category, the path to championship success - based on this performance - still looks steep.
Hatton Homage Inspires Local Rivalry Battle
In the co-main event, Arthur overcame Bradley Rea by split-decision in a excellent all-Manchester contest to win the European light heavyweight championship.
The arena grew hushed for a profoundly moving tribute prior to the bout as ten bells rang in memory of Manchester's own Ricky Hatton, who passed away aged 46 in recently.
It was the premier televised fight night in the city since the passing of Hatton. As the final chime disappeared, the stillness gave way to a shout of "only one Hatton".
The competition within the ring reflected the sentiment. Arthur was knocked down by a left hook directly to the jaw in the initial stage, standing uncertainly to his position on the referee's count.
But the Manchester United-red shorts of Arthur soon pressed ahead again. On the opposite side, Rea - in rival City blue - was injured quickly, significant bruising appearing under his face as the fighters landed powerful shots.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with effective uppercuts as the action seldom decreased over 12 rounds.
The victor narrowly won the decision with official scores of even score, narrow lead and wider gap, but each competitor were determined and brave, exactly what their idol the legend stood for.
