British light heavyweight Joshua Buatsi secured a victory yet underwhelming debut to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a close 10-round bout at the Manchester venue.
But the challenger found success, landing some telling individual punches in a match where the techniques never quite clicked, with constant grabbing disrupting the contest.
Two judges judged it 96-94 for to the winner, with the final judge a even score.
"It wasn't my greatest display but what defines champions? They prevail," the victor said in the ringside as he was met by boos from the spectators.
The British fighter got back to winning after his initial pro loss - an epic battle with Callum Smith in February - to secure a 20th career victory.
Some ringside observers thought Parker, thirty-one, deserved the decision but the Derbyshire fighter experienced the second loss of his 28-bout career.
The Champion Claims Victory in Slow Encounter
His career development has plateaued in the past few years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the future of British boxing, he now stands trying to fulfil that early promise - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers willing to overcommit in a tentative early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand during the bout, was participating in his second appearance at light heavyweight.
By the middle rounds, Parker had stayed in contention, creating difficulties for Buatsi, who utilized a protective stance to barely take the better periods.
The spectators' acceptance diminished because of frequent holding, with Parker slipping to the canvas several times during close exchanges.
The underdog ended stronger, but many rounds were hard to judge. Nevertheless, former world champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
The victor advances, but with the presence of hard hitter Benavidez, and Russian champion Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Hatton Memorial Inspires Manchester Derby Contest
In the secondary fight, Lyndon Arthur defeated Rea by split-decision in a terrific local rivalry fight to win the European light-heavyweight belt.
The venue grew hushed for a profoundly moving tribute before the fight as 10 bells sounded in remembrance of the city's native Hatton, who died aged 46 in last month.
It was the first major televised fight night in the urban center since the passing of Hatton. As the concluding sound faded, the stillness became a shout of "there's just one Hatton".
The competition inside the ropes matched the sentiment. Arthur was floored by a left hook squarely on the chin in the second round, standing uncertainly to his feet on the eight count.
But the traditional red shorts of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was damaged quickly, noticeable damage developing under his orbital area as the duo traded powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the pace rarely dropped over 12 rounds.
Arthur edged the verdict with scoring tallies of draw, close margin and 115-112, but each competitor were relentless and brave, exactly what their idol Hatton stood for.
