UK light heavyweight Joshua Buatsi earned a win yet unimpressive start to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a majority decision in a close ten-round fight at the Manchester venue.
But Parker had his moments, connecting with powerful individual punches in a contest where the approaches failed to mesh, with constant grabbing marring the fight.
The officials judged it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my greatest performance but how do champions respond? They win," Buatsi commented in the arena as he was greeted with disapproval from the audience.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in February - to claim a 20th career victory.
Several boxing experts believed Parker, 31, merited the decision but the Derbyshire fighter suffered the second defeat of his 28-match career.
The Champion Secures Triumph in Dull Match
The fighter's advancement has plateaued in recent years through management issues and long spells of inactivity.
Earlier forecast as the future of British boxing, he now is positioned trying to achieve expectations - perhaps in what appears to be a last chance - under fresh management.
He started carefully, with both competitors ready to be aggressive in a cagey opening few rounds.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was competing in only his second appearance at light-heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for Buatsi, who utilized a solid defense to narrowly win the more effective stanzas.
The spectators' acceptance diminished because of frequent holding, with Parker slipping to the canvas multiple occasions during close exchanges.
Parker closed well, but many rounds were hard to judge. Although, previous titleholder the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just a single round.
The victor progresses, but with the likes of power puncher David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still looks steep.
Hatton Tribute Fuels All-Manchester Battle
In the secondary fight, Lyndon Arthur defeated Rea by close verdict in a outstanding all-Manchester contest to win the European light-heavyweight championship.
The venue fell silent for a deeply poignant tribute before the fight as 10 bells rang in memory of local hero Hatton, who passed away aged 46 in September.
It was the initial significant broadcast boxing event in the urban center since Hatton's death. As the final chime disappeared, the quiet became a chant of "only one Ricky Hatton".
The action inside the ropes equaled the emotion. Arthur was knocked down by a powerful punch squarely on the face in the early round, standing uncertainly to his position on the referee's count.
But the traditional red shorts of the fighter soon came forward again. On the opposite side, Rea - in competitive blue - was damaged soon, heavy swelling forming under his eye as the duo traded punishing blows.
Rea, 27, landed power punches but Arthur, thirty-four, fought fire with fire with powerful upward punches as the pace seldom decreased over twelve rounds.
The victor barely secured the result with judges scorecards of draw, 115-113 and wider gap, but each competitor were persistent and brave, exactly what their inspiration the legend represented.
