UK light-heavyweight Joshua Buatsi made a winning yet unimpressive start to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a close ten-round contest at the Co-op Live Arena.
But Parker found success, connecting with powerful single shots in a contest where the styles failed to mesh, with constant grabbing disrupting the fight.
The scoring judges had it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my greatest display but what defines champions? They succeed," Buatsi said in the arena as he was greeted with boos from the spectators.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in last winter - to earn a twentieth professional win.
Several boxing experts thought Parker, 31, should have been awarded the decision but the British boxer experienced the second setback of his 28-bout career.
Buatsi's progress has stalled in recent times through management issues and considerable time of lack of fights.
Once tipped as the rising talent of the British fight scene, he now stands trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under recent support.
He began cautiously, with the two boxers ready to take risks in a cagey initial rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was competing in only his second bout at the higher weight class.
By the middle rounds, Parker had stayed in contention, creating difficulties for the favorite, who operated with a tight guard to edge the more effective stanzas.
The audience's tolerance diminished during frequent holding, with Parker going down various instances during grappling.
The underdog finished the stronger, but many rounds were hard to judge. Nevertheless, former world champion Carl Frampton - commentating on Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
Buatsi advances, but with the caliber of power puncher Benavidez, and Russian star Bivol leading the category, the journey to titles - on this evidence - still appears challenging.
In the co-main event, Lyndon Arthur overcame Rea by divided decision in a excellent Manchester vs Manchester contest to secure the continental title.
The arena became quiet for a profoundly moving homage before the fight as a bell ceremony tolled in memory of the city's native Ricky Hatton, who died at age 46 in recently.
It was the premier televised match card in the urban center since Hatton's death. As the final chime faded, the quiet became a shout of "there's just one Ricky Hatton".
The fighting within the ring equaled the feeling. The eventual winner was floored by a left hook squarely on the chin in the second round, rising shakily to his footing on the referee's count.
But the Manchester United-red attire of the fighter soon pressed ahead again. From the other corner, the opponent - in competitive blue - was injured soon, significant bruising developing under his eye as the fighters traded powerful shots.
Rea, 27, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the action seldom decreased over twelve rounds.
Arthur barely secured the decision with official scores of draw, close margin and wider gap, but each competitor were determined and full of heart, exactly what their hero Hatton stood for.
Liam is a professional esports analyst and gaming enthusiast with over 10 years of experience in the industry.