British light-heavyweight Joshua Buatsi secured a victory yet disappointing debut to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a close ten-round bout at the Manchester venue.
But the challenger found success, landing some telling individual punches in a fight where the styles failed to mesh, with excessive holding disrupting the action.
The scoring judges had it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my best showing but what do champions do? They win," Buatsi commented in the arena as he was greeted with boos from the crowd.
The Londoner bounced back after his first professional defeat - an epic battle with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts felt Parker, thirty-one, deserved the victory but the Derbyshire fighter experienced the second defeat of his 28-match professional journey.
Buatsi Claims Win in Dull Match
The fighter's advancement has plateaued in recent times through management issues and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now stands trying to realize his potential - perhaps in what seems like a last chance - under new promotional backing.
He began cautiously, with neither fighter ready to overcommit in a cagey opening few rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was participating in his second fight at light-heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for Buatsi, who worked behind a solid defense to barely take the more effective stanzas.
The spectators' acceptance decreased because of regular grabbing, with Parker going down several times during clinches.
Parker closed well, but multiple periods were challenging to assess. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
The victor moves on, but with the likes of power puncher Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Homage Motivates All-Manchester Contest
In the supporting bout, Lyndon Arthur defeated Rea by close verdict in a outstanding all-Manchester fight to secure the European light-heavyweight championship.
The venue grew hushed for a extremely emotional memorial prior to the bout as 10 bells sounded in honor of the city's native Ricky Hatton, who succumbed 46 years old in last month.
It was the premier televised boxing event in the location since Hatton's passing. As the final chime ended, the silence became a chant of "there's just one Hatton".
The fighting during the bout reflected the sentiment. Arthur was knocked down by a left hook flush on the chin in the early round, rising shakily to his position on the referee's count.
But the traditional red attire of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was marked up soon, significant bruising appearing under his face as the pair exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with effective uppercuts as the intensity seldom decreased over the full distance.
The victor narrowly won the decision with judges scorecards of even score, narrow lead and clearer margin, but both fighters were relentless and full of heart, everything their inspiration the legend stood for.
