UK light heavyweight Joshua Buatsi made a winning yet unimpressive start to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a close 10-round bout at the Manchester venue.
But Parker had his moments, delivering effective clean blows in a match where the styles didn't complement each other, with excessive holding spoiling the contest.
The officials judged it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my best display but what do champions do? They prevail," Buatsi stated in the ringside as he was faced negative reactions from the crowd.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Various analysts felt Parker, thirty-one, merited the decision but the British boxer endured the second loss of his 28-fight career.
Buatsi Earns Triumph in Dull Match
The fighter's advancement has stalled in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the rising talent of UK boxing, he now stands trying to fulfil that early promise - perhaps in what appears to be a ultimate opportunity - under fresh management.
He began cautiously, with the two boxers willing to take risks in a calculated opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was participating in his second bout at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for Buatsi, who worked behind a protective stance to edge the more effective stanzas.
The crowd's patience decreased amid frequent holding, with Parker falling to the floor various instances during grappling.
Parker closed well, but many rounds were difficult to score. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it strongly leaning for Parker, scoring for Buatsi just one round.
The victor moves on, but with the presence of power puncher Benavidez, and Russian star Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Homage Fuels Local Rivalry Fight
In the co-main event, Lyndon Arthur overcame Rea by split-decision in a excellent Manchester vs Manchester battle to capture the continental belt.
The arena grew hushed for a profoundly moving tribute before the fight as a bell ceremony tolled in memory of the city's native Ricky Hatton, who died 46 years old in recently.
It was the first major televised match card in the urban center since the passing of Hatton. As the last bell faded, the silence gave way to a roar of "there's only one Ricky Hatton".
The competition inside the ropes equaled the feeling. Arthur was floored by a left hook directly to the face in the second round, rising shakily to his footing on the referee's count.
But the traditional red attire of Arthur soon came forward again. On the opposite side, Rea - in opposing blue - was injured soon, heavy swelling forming under his eye as the duo exchanged punishing blows.
Rea, 27, landed power punches but the champion, 34, responded in kind with effective uppercuts as the pace hardly diminished over twelve rounds.
Arthur narrowly won the decision with judges scorecards of even score, 115-113 and 115-112, but each competitor were persistent and brave, exactly what their hero the legend represented.
