UK light heavyweight Joshua Buatsi earned a win yet unimpressive debut to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a majority decision in a close ten-round bout at the Manchester venue.
But the challenger landed significant shots, connecting with powerful clean blows in a fight where the styles failed to mesh, with constant grabbing disrupting the action.
Two judges judged it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my best showing but what defines champions? They succeed," Buatsi said in the ring as he was met by negative reactions from the crowd.
The British fighter bounced back after his initial pro loss - an thrilling contest with Callum Smith in February - to earn a 20th pro success.
Several boxing experts thought the challenger, thirty-one, merited the win but the Derbyshire fighter experienced the second setback of his 28-bout professional journey.
The Champion Secures Win in Uneventful Match
His career development has plateaued in recent years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the rising talent of British boxing, he now stands trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under recent support.
He began cautiously, with both competitors ready to take risks in a cagey opening few rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, 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 protective stance to edge the cleaner rounds.
The crowd's patience diminished amid regular grabbing, with Parker falling to the floor multiple occasions during close exchanges.
The underdog ended stronger, but several stanzas were difficult to score. Although, ex-champion the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
Buatsi advances, but with the likes of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still seems difficult.
Hatton Memorial Motivates Manchester Derby Contest
In the secondary fight, Lyndon Arthur overcame Rea by split-decision in a outstanding local rivalry battle to capture the European light-heavyweight title.
The stadium became quiet for a extremely emotional homage before the fight as 10 bells sounded in honor of local hero Ricky Hatton, who succumbed aged 46 in recently.
It was the premier televised match card in the city since Hatton's death. As the concluding sound faded, the quiet transitioned to a roar of "there's just one Ricky Hatton".
The fighting within the ring reflected the feeling. Arthur was floored by a powerful punch flush on the chin in the second round, standing uncertainly to his position on the count of eight.
But the red-colored equipment of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was marked up soon, heavy swelling forming under his face as the pair traded hard punches.
Rea, twenty-seven, landed power punches but the champion, 34, responded in kind with effective uppercuts as the pace hardly diminished over 12 rounds.
Arthur narrowly won the decision with official scores of even score, narrow lead and 115-112, but each competitor were determined and full of heart, everything their hero Hatton represented.
