British light heavyweight Joshua Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a split decision in a close 10-round bout at the Manchester venue.
But the challenger found success, connecting with powerful clean blows in a fight where the techniques failed to mesh, with constant grabbing disrupting the fight.
Two judges judged it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best showing but what do champions do? They prevail," the victor commented in the ringside as he was faced disapproval from the audience.
The Londoner returned to winning ways after his initial pro loss - an epic battle with his previous opponent in last winter - to claim a 20th career victory.
Several boxing experts thought the challenger, 31, should have been awarded the win but the contender experienced the second defeat of his 28-match career.
Buatsi Earns Triumph in Slow Encounter
His career development has plateaued in the past few years through promotional disputes and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter ready to take risks in a tentative early stages.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after breaking his hand during the bout, was making just his second bout at light-heavyweight.
By the halfway stage, Parker had stayed in contention, creating difficulties for Buatsi, who utilized a tight guard to edge the more effective periods.
The spectators' acceptance diminished because of constant clinching, with the challenger falling to the floor various instances during clinches.
The underdog ended stronger, but many rounds were hard to judge. However, previous titleholder Carl Frampton - working with Dazn - had it strongly leaning for Parker, awarding Buatsi just one round.
The victor progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Hatton Homage Motivates All-Manchester Battle
In the secondary fight, Lyndon Arthur beat Rea by close verdict in a outstanding all-Manchester contest to secure the European light-heavyweight title.
The arena became quiet for a profoundly moving memorial ahead of the contest as a bell ceremony sounded in memory of local hero Ricky Hatton, who passed away at age 46 in recently.
It was the first major televised boxing event in the location since the passing of Hatton. As the final chime disappeared, the silence gave way to a roar of "there's just one Hatton".
The competition inside the ropes matched the feeling. Arthur was knocked down by a powerful punch squarely on the jaw in the early round, rising shakily to his footing on the count of eight.
But the red-colored equipment of the fighter soon pressed ahead again. Across the ring, Rea - in competitive blue - was marked up soon, significant bruising forming under his eye as the duo landed powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with stinging uppercuts as the intensity rarely dropped over twelve rounds.
The victor barely secured the decision with scoring tallies of 114-114, 115-113 and 115-112, but each competitor were determined and courageous, exactly what their hero the legend embodied.
