British light-heavyweight Joshua Buatsi secured a victory yet underwhelming debut to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a split decision in a tight ten-round contest at the Manchester venue.
But Parker landed significant shots, delivering effective clean blows in a contest where the styles failed to mesh, with frequent clinching marring the action.
Two judges scored it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest performance but what defines champions? They succeed," the victor stated in the ringside as he was greeted with negative reactions from the spectators.
The British fighter got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a 20th pro success.
Various analysts felt Parker, thirty-one, deserved the decision but the Derbyshire fighter suffered the second loss of his 28-bout professional journey.
Buatsi Claims Win in Slow Affair
His career development has plateaued in the past few years through promotional disputes and considerable time of inactivity.
Once tipped as the next star of British boxing, he now finds himself trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under fresh management.
He started carefully, with both competitors prepared to take risks in a tentative early stages.
The challenger, whose single earlier setback came at super middleweight against his former opponent in 2022 after damaging his hand in the contest, was competing in only his second bout at the higher weight class.
By the halfway stage, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a solid defense to barely take the cleaner periods.
The audience's tolerance diminished because of regular grabbing, with the challenger slipping to the canvas various instances during clinches.
Parker ended stronger, but multiple periods were difficult to score. However, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, giving Buatsi just a single round.
The victor advances, but with the presence of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Tribute Fuels Manchester Derby Fight
In the co-main event, Lyndon Arthur defeated Bradley Rea by close verdict in a terrific all-Manchester fight to win the European light heavyweight championship.
The venue fell silent for a deeply poignant homage before the fight as a bell ceremony rang in honor of Manchester's own Ricky Hatton, who succumbed 46 years old in last month.
It was the premier televised match card in the city since the passing of Hatton. As the concluding sound disappeared, the silence became a shout of "there's only one Hatton".
The competition inside the ropes equaled the feeling. The eventual winner was floored by a powerful punch squarely on the face in the early round, standing uncertainly to his footing on the eight count.
But the red-colored equipment of the fighter soon advanced again. On the opposite side, the opponent - in competitive blue - was damaged quickly, noticeable damage developing under his eye as the fighters landed powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with effective uppercuts as the pace seldom decreased over twelve rounds.
Arthur narrowly won the result with official scores of 114-114, narrow lead and wider gap, but each competitor were relentless and full of heart, everything their inspiration Hatton stood for.
