UK light-heavyweight Joshua Buatsi secured a victory yet disappointing beginning to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a split decision in a competitive 10-round bout at the Manchester venue.
But the challenger had his moments, delivering effective single shots in a match where the approaches didn't complement each other, with constant grabbing spoiling the contest.
The officials scored it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best showing but how do champions respond? They win," Buatsi commented in the ring as he was faced disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in last winter - to earn a 20th pro success.
Various analysts felt the challenger, 31, merited the win but the British boxer suffered the second setback of his 28-fight professional journey.
The Champion Earns Triumph in Dull Match
Buatsi's progress has plateaued in recent times through promotional disputes and considerable time of inactivity.
Previously predicted as the future of UK boxing, he now finds himself trying to achieve expectations - maybe in what seems like a last chance - under fresh management.
He started carefully, with neither fighter willing to overcommit in a tentative early stages.
Parker, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, 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 operated with a protective stance to edge the better stanzas.
The audience's tolerance decreased because of constant clinching, with Parker slipping to the canvas multiple occasions during grappling.
Parker finished the stronger, but multiple periods were difficult to score. Nevertheless, former world champion the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just only one stanza.
Buatsi moves on, but with the caliber of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Homage Fuels Local Rivalry Contest
In the co-main event, Arthur beat Rea by split-decision in a terrific Manchester vs Manchester battle to win the European light-heavyweight title.
The venue grew hushed for a profoundly moving memorial before the fight as 10 bells sounded in remembrance of the city's native Ricky Hatton, who died at age 46 in recently.
It was the premier televised fight night in the urban center since the passing of Hatton. As the last bell disappeared, the stillness transitioned to a shout of "there's only one Ricky Hatton".
The competition inside the ropes matched the feeling. The eventual winner was knocked down by a significant blow directly to the jaw in the early round, standing uncertainly to his position on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. Across the ring, Rea - in rival City blue - was marked up quickly, significant bruising developing under his eye as the duo exchanged powerful shots.
The challenger, twenty-seven, landed power punches but the champion, 34, responded in kind with stinging uppercuts as the pace seldom decreased over 12 rounds.
The victor narrowly won the verdict with official scores of draw, close margin and clearer margin, but each competitor were persistent and brave, all the qualities their hero the legend stood for.
