British light heavyweight Joshua Buatsi earned a win yet unimpressive beginning 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 Manchester venue.
But Parker had his moments, delivering effective clean blows in a match where the approaches didn't complement each other, with frequent clinching spoiling the action.
The scoring judges judged it 96-94 to the winner, with the third a even score.
"It wasn't my finest performance but what defines champions? They prevail," Buatsi said in the arena as he was greeted with negative reactions from the spectators.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in last winter - to claim a twentieth professional win.
Several boxing experts thought the challenger, 31, should have been awarded the victory but the British boxer experienced the second loss of his 28-fight career.
The Champion Secures Victory in Dull Encounter
The fighter's advancement has stalled in the past few years through management issues and considerable time of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now stands trying to achieve expectations - maybe in what feels like a last chance - under fresh management.
He began cautiously, with neither fighter prepared to overcommit in a tentative initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was competing in only his second fight at the higher weight class.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who operated with a tight guard to barely take the better rounds.
The audience's tolerance decreased during constant clinching, with Parker going down various instances during clinches.
Parker ended stronger, but multiple periods were challenging to assess. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
The victor advances, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - on this evidence - still looks steep.
Hatton Tribute Fuels All-Manchester Contest
In the supporting bout, Lyndon Arthur beat Rea by divided decision in a excellent Manchester vs Manchester contest to capture the European light heavyweight title.
The venue fell silent for a extremely emotional homage before the fight as a bell ceremony rang in memory of the city's native Ricky Hatton, who passed away 46 years old in September.
It was the premier televised match card in the urban center since Hatton's death. As the concluding sound disappeared, the silence gave way to a roar of "there's just one Ricky Hatton".
The competition during the bout equaled the sentiment. Arthur was sent to the canvas by a powerful punch directly to the chin in the initial stage, getting up unsteadily to his footing on the count of eight.
But the Manchester United-red attire of Arthur soon came forward again. Across the ring, Rea - in rival City blue - was damaged soon, noticeable damage forming under his orbital area as the fighters landed hard punches.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the pace hardly diminished over the full distance.
The victor edged the verdict with judges scorecards of even score, close margin and wider gap, but both fighters were persistent and courageous, all the qualities their hero Hatton embodied.
