British light heavyweight Joshua Buatsi secured a victory yet unimpressive debut to life under fresh promotional backing with a unanimous decision 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 boxing arena.
But Parker had his moments, landing some telling individual punches in a contest where the approaches failed to mesh, with constant grabbing marring the action.
The scoring judges had it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest showing but what do champions do? They win," the victor commented in the ring as he was met by boos from the spectators.
The British fighter bounced back after his initial pro loss - an epic battle with Callum Smith in last winter - to secure a 20th pro success.
Various analysts felt the challenger, 31, deserved the win but the British boxer endured the second loss of his 28-bout professional journey.
The Champion Earns Victory in Slow Match
The fighter's advancement has slowed in the past few years through promotional disputes and considerable time of inactivity.
Previously predicted as the future of UK boxing, he now stands trying to realize his potential - maybe in what seems like a final roll of the dice - under recent support.
He began cautiously, with neither fighter prepared to overcommit 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 during the bout, was making just his second appearance at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for Buatsi, who worked behind a protective stance to barely take the better stanzas.
The crowd's patience decreased during constant clinching, with Parker slipping to the canvas multiple occasions during clinches.
Parker closed well, but multiple periods were difficult to score. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just a single round.
The victor advances, but with the likes of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - on this evidence - still appears challenging.
Hatton Homage Fuels Manchester Derby Fight
In the supporting bout, Lyndon Arthur defeated Rea by split-decision in a outstanding all-Manchester contest to win the European light heavyweight championship.
The arena grew hushed for a profoundly moving tribute prior to the bout as 10 bells tolled in memory of the city's native Ricky Hatton, who succumbed aged 46 in September.
It was the premier televised boxing event in the location since Hatton's death. As the last bell disappeared, the stillness transitioned to a shout of "only one Hatton".
The fighting within the ring matched the emotion. Arthur was sent to the canvas by a powerful punch flush on the face in the initial stage, rising shakily to his feet on the eight count.
But the traditional red shorts of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was marked up soon, significant bruising forming under his face as the pair exchanged punishing blows.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with effective uppercuts as the intensity seldom decreased over the full distance.
The victor edged the decision with official scores of draw, 115-113 and wider gap, but the two athletes were relentless and courageous, all the qualities their hero the legend embodied.
