UK light-heavyweight Joshua Buatsi secured a victory yet unimpressive beginning to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a split decision in a competitive ten-round contest at the Manchester venue.
But the challenger landed significant shots, connecting with powerful individual punches in a match where the approaches didn't complement each other, with constant grabbing spoiling the contest.
The officials had it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my best display but how do champions respond? They win," the victor commented in the arena as he was met by negative reactions from the crowd.
The British fighter bounced back after his initial pro loss - an epic battle with his previous opponent in last winter - to claim a twentieth professional win.
Several boxing experts believed the challenger, 31, should have been awarded the victory but the Derbyshire fighter suffered the second defeat of his 28-match professional journey.
Buatsi Secures Win in Uneventful Match
The fighter's advancement has slowed in recent years through promotional disputes and long spells of inactivity.
Once tipped as the future of the British fight scene, he now finds himself trying to realize his potential - maybe in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with the two boxers ready to be aggressive in a calculated initial rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in 2022 after damaging his hand mid-fight, was making just his second fight at the higher weight class.
By the middle rounds, Parker had made it competitive, making life awkward for Buatsi, who operated with a solid defense to narrowly win the more effective rounds.
The audience's tolerance decreased because of constant clinching, with the challenger slipping to the canvas several times during grappling.
Parker ended stronger, but multiple periods were hard to judge. Nevertheless, ex-champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
The victor advances, but with the likes of power puncher Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Memorial Fuels All-Manchester Fight
In the co-main event, Lyndon Arthur overcame Bradley Rea by divided decision in a excellent Manchester vs Manchester fight to win the European light-heavyweight belt.
The stadium grew hushed for a profoundly moving tribute ahead of the contest as 10 bells tolled in remembrance of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the first major televised fight night in the city since Hatton's passing. As the last bell faded, the stillness gave way to a roar of "there's just one Ricky Hatton".
The competition within the ring matched the emotion. The eventual winner was knocked down by a significant blow directly to the chin in the early round, rising shakily to his footing on the count of eight.
But the red-colored equipment of Arthur soon pressed ahead again. Across the ring, Rea - in opposing blue - was injured quickly, significant bruising appearing under his eye as the fighters traded powerful shots.
Rea, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with effective uppercuts as the pace seldom decreased over twelve rounds.
Arthur edged the result with judges scorecards of 114-114, 115-113 and wider gap, but the two athletes were persistent and brave, everything their inspiration the legend represented.
