UK light heavyweight Joshua Buatsi secured a victory yet disappointing debut to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a close 10-round contest at the boxing arena.
But Parker landed significant shots, landing some telling individual punches in a fight where the techniques didn't complement each other, with frequent clinching disrupting the fight.
The scoring judges judged it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my best display but what defines champions? They win," Buatsi commented in the ringside as he was greeted with negative reactions from the audience.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to secure a 20th pro success.
Some ringside observers thought Parker, thirty-one, merited the decision but the British boxer endured the second loss of his 28-match professional journey.
The Champion Secures Victory in Dull Encounter
The fighter's advancement has stalled in recent years through promotional disputes and long spells of inactivity.
Previously predicted as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers ready to take risks in a cagey opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was competing in only his second appearance at light heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a tight guard to edge the better periods.
The audience's tolerance decreased during regular grabbing, with the challenger going down several times during close exchanges.
The underdog ended stronger, but several stanzas were difficult to score. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor progresses, but with the presence of power puncher David Benavidez, and Russian star Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Tribute Inspires Local Rivalry Fight
In the secondary fight, Lyndon Arthur beat Rea by divided decision in a excellent all-Manchester battle to secure the European light heavyweight belt.
The venue became quiet for a deeply poignant memorial prior to the bout as 10 bells tolled in remembrance of the city's native Ricky Hatton, who died at age 46 in September.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the concluding sound faded, the silence transitioned to a roar of "there's just one Ricky Hatton".
The fighting inside the ropes matched the feeling. Arthur was floored by a significant blow directly to the chin in the early round, standing uncertainly to his footing on the count of eight.
But the traditional red attire of Arthur soon came forward again. Across the ring, the opponent - in rival City blue - was injured soon, noticeable damage appearing under his orbital area as the fighters exchanged punishing blows.
Rea, 27, landed power punches but the champion, thirty-four, responded in kind with effective uppercuts as the action hardly diminished over the full distance.
The victor narrowly won the result with judges scorecards of even score, 115-113 and wider gap, but the two athletes were relentless and courageous, exactly what their idol the legend embodied.
