UK light heavyweight Joshua Buatsi earned a win yet unimpressive start to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a competitive ten-round bout at the Co-op Live Arena.
But Parker landed significant shots, delivering effective individual punches in a fight where the techniques failed to mesh, with excessive holding disrupting the action.
Two judges judged it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my finest performance but what defines champions? They prevail," the victor commented in the arena as he was met by disapproval from the crowd.
The Londoner bounced back after his first professional defeat - an epic battle with his previous opponent in last winter - to claim a twentieth professional win.
Various analysts believed Parker, 31, merited the victory but the British boxer endured the second loss of his 28-fight professional journey.
Buatsi Secures Victory in Uneventful Encounter
The fighter's advancement has stalled in recent years through contract problems and long spells of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now stands trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers ready to take risks in a tentative early stages.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand in the contest, was making just his second fight at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for the favorite, who utilized a solid defense to narrowly win the more effective periods.
The audience's tolerance diminished because of regular grabbing, with Parker slipping to the canvas various instances during grappling.
The underdog finished the stronger, but many rounds were difficult to score. Although, former world champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just a single round.
The victor progresses, but with the likes of power puncher Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Tribute Fuels All-Manchester Contest
In the secondary fight, Lyndon Arthur defeated Bradley Rea by divided decision in a excellent local rivalry battle to win the European light heavyweight title.
The venue grew hushed for a profoundly moving tribute ahead of the contest as a bell ceremony tolled in honor of the city's native Hatton, who passed away at age 46 in September.
It was the first major televised match card in the location since Hatton's death. As the concluding sound disappeared, the quiet became a shout of "there's just one Hatton".
The fighting inside the ropes matched the sentiment. The eventual winner was sent to the canvas by a left hook directly to the chin in the initial stage, standing uncertainly to his feet on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was damaged soon, significant bruising developing under his orbital area as the duo traded punishing blows.
The challenger, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with stinging uppercuts as the action hardly diminished over twelve rounds.
Arthur barely secured the result with scoring tallies of even score, close margin and 115-112, but each competitor were relentless and brave, exactly what their inspiration the legend represented.
