British light heavyweight Joshua Buatsi made a winning yet disappointing debut to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a competitive ten-round contest at the Manchester venue.
But Parker landed significant shots, connecting with powerful individual punches in a match where the techniques failed to mesh, with constant grabbing spoiling the fight.
Two judges scored it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest display but how do champions respond? They prevail," the victor said in the arena as he was met by disapproval from the spectators.
The Londoner bounced back after his first professional defeat - an thrilling contest with his previous opponent in February - to claim a twentieth professional win.
Some ringside observers thought Parker, 31, should have been awarded the win but the contender experienced the second defeat of his 28-bout career.
The Champion Earns Victory in Uneventful Match
His career development has plateaued in recent years through contract problems and considerable time of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now finds himself trying to realize his potential - maybe in what feels like a last chance - under recent support.
He opened tentatively, with the two boxers willing to overcommit in a tentative early stages.
Parker, whose only previous defeat came at super middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was participating in his second fight at the higher weight class.
By the halfway stage, Parker had stayed in contention, creating difficulties for Buatsi, who worked behind a solid defense to narrowly win the better stanzas.
The spectators' acceptance diminished amid regular grabbing, with the challenger falling to the floor several times during clinches.
The underdog ended stronger, but several stanzas were challenging to assess. Nevertheless, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
The victor advances, but with the likes of heavy hitter Benavidez, and Russian champion Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Hatton Tribute Inspires All-Manchester Contest
In the supporting bout, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific all-Manchester fight to win the European light-heavyweight championship.
The stadium became quiet for a extremely emotional memorial before the fight as ten bells tolled in honor of Manchester's own Hatton, who died 46 years old in recently.
It was the first major televised match card in the location since the passing of Hatton. As the concluding sound disappeared, the silence gave way to a shout of "only one Hatton".
The competition inside the ropes matched the emotion. Arthur was sent to the canvas by a significant blow squarely on the face in the second round, rising shakily to his footing on the referee's count.
But the Manchester United-red shorts of the fighter soon pressed ahead again. Across the ring, the opponent - in rival City blue - was marked up early, significant bruising forming under his orbital area as the pair traded punishing blows.
The challenger, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with stinging uppercuts as the intensity seldom decreased over twelve rounds.
The victor barely secured the result with scoring tallies of even score, 115-113 and clearer margin, but each competitor were persistent and courageous, exactly what their hero the legend stood for.
