British light heavyweight Joshua Buatsi earned a win yet underwhelming debut to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a split decision in a close 10-round bout at the boxing arena.
But the challenger found success, delivering effective single shots in a contest where the approaches failed to mesh, with constant grabbing spoiling the fight.
Two judges scored it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my finest display but what defines champions? They succeed," Buatsi said in the ring as he was faced disapproval from the crowd.
The British fighter got back to winning after his first professional defeat - an epic battle with Callum Smith in February - to claim a 20th career victory.
Some ringside observers thought the challenger, 31, should have been awarded the victory but the Derbyshire fighter endured the second defeat of his 28-fight career.
Buatsi Secures Triumph in Uneventful Encounter
The fighter's advancement has stalled in recent times through management issues and considerable time of inactivity.
Once tipped as the next star of the British fight scene, he now stands trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under recent support.
He began cautiously, with neither fighter ready to take risks in a cagey early stages.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was making just his second appearance at the higher weight class.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who worked behind a protective stance to edge the better stanzas.
The audience's tolerance decreased during regular grabbing, with Parker falling to the floor various instances during grappling.
The underdog finished the stronger, but multiple periods were challenging to assess. Nevertheless, ex-champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, giving Buatsi just one round.
The victor advances, but with the caliber of heavy hitter Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Hatton Memorial Fuels Manchester Derby Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a excellent Manchester vs Manchester fight to capture the European light-heavyweight championship.
The venue became quiet for a deeply poignant tribute prior to the bout as ten bells sounded in honor of Manchester's own Ricky Hatton, who died at age 46 in recently.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the concluding sound faded, the silence transitioned to a shout of "only one Hatton".
The fighting within the ring reflected the emotion. Arthur was knocked down by a left hook directly to the chin in the second round, getting up unsteadily to his footing on the referee's count.
But the traditional red attire of the fighter soon pressed ahead again. From the other corner, Rea - in opposing blue - was injured quickly, noticeable damage forming under his face as the duo exchanged hard punches.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with stinging uppercuts as the intensity hardly diminished over twelve rounds.
The victor narrowly won the verdict with official scores of 114-114, close margin and wider gap, but both fighters were relentless and courageous, exactly what their inspiration the legend embodied.
