British light heavyweight Joshua Buatsi made a winning yet disappointing start to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a competitive ten-round bout at the Manchester venue.
But Parker found success, landing some telling clean blows in a match where the approaches failed to mesh, with excessive holding disrupting the fight.
The officials had it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They prevail," the victor stated in the arena as he was faced boos from the audience.
The British fighter bounced back after his first professional defeat - an memorable fight with Callum Smith in last winter - to claim a 20th pro success.
Several boxing experts felt the challenger, thirty-one, should have been awarded the victory but the British boxer suffered the second defeat of his 28-fight professional journey.
Buatsi Earns Win in Dull Affair
Buatsi's progress has plateaued in the past few years through promotional disputes and considerable time of inactivity.
Once tipped as the future of British boxing, he now stands trying to realize his potential - maybe in what seems like a ultimate opportunity - under recent support.
He began cautiously, with neither fighter prepared to be aggressive in a cagey initial rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after damaging his hand in the contest, was participating in his second fight at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for Buatsi, who worked behind a tight guard to edge the more effective stanzas.
The audience's tolerance wore thin amid regular grabbing, with Parker falling to the floor several times during clinches.
Parker ended stronger, but multiple periods were hard to judge. However, former world champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
The victor advances, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Hatton Homage Fuels Manchester Derby Battle
In the supporting bout, Arthur overcame Rea by split-decision in a outstanding local rivalry battle to capture the continental belt.
The stadium grew hushed for a deeply poignant homage ahead of the contest as ten bells tolled in honor of local hero Hatton, who passed away aged 46 in September.
It was the initial significant broadcast fight night in the location since Hatton's death. As the concluding sound ended, the silence transitioned to a roar of "there's just one Hatton".
The fighting during the bout equaled the feeling. Arthur was knocked down by a significant blow directly to the jaw in the initial stage, rising shakily to his position on the eight count.
But the Manchester United-red attire of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was damaged quickly, significant bruising forming under his face as the duo exchanged powerful shots.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with effective uppercuts as the action rarely dropped over the full distance.
The victor narrowly won the result with official scores of 114-114, close margin and wider gap, but each competitor were relentless and full of heart, everything their hero the legend represented.
