UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming debut to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a tight 10-round bout at the Manchester venue.
But the challenger landed significant shots, delivering effective clean blows in a match where the techniques didn't complement each other, with frequent clinching spoiling the contest.
The scoring judges judged it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my finest display but what defines champions? They prevail," Buatsi stated in the ringside as he was met by boos from the crowd.
The British fighter got back to winning after his first professional defeat - an epic battle with Callum Smith in February - to earn a twentieth professional win.
Various analysts thought the challenger, 31, deserved the victory but the Derbyshire fighter experienced the second defeat of his 28-fight professional journey.
The Champion Earns Victory in Dull Affair
Buatsi's progress has plateaued in recent times through contract problems and long spells of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to realize his potential - perhaps in what feels like a last chance - under new promotional backing.
He started carefully, with the two boxers 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 during the bout, was competing in only his second bout at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who worked behind a tight guard to barely take the better periods.
The spectators' acceptance decreased during regular grabbing, with Parker falling to the floor multiple occasions during grappling.
The underdog closed well, but many rounds were difficult to score. Nevertheless, previous titleholder the boxing analyst - commentating on Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Homage Motivates Local Rivalry Fight
In the secondary fight, Lyndon Arthur defeated Bradley Rea by divided decision in a excellent Manchester vs Manchester fight to win the European light heavyweight title.
The venue became quiet for a deeply poignant tribute before the fight as ten bells tolled in memory of Manchester's own Hatton, who died aged 46 in recently.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the concluding sound ended, the quiet became a shout of "only one Ricky Hatton".
The action within the ring matched the feeling. The eventual winner was sent to the canvas by a significant blow directly to the jaw in the second round, standing uncertainly to his footing on the count of eight.
But the red-colored attire of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was damaged soon, significant bruising developing under his orbital area as the fighters landed punishing blows.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with powerful upward punches as the pace rarely dropped over twelve rounds.
Arthur barely secured the verdict with scoring tallies of draw, 115-113 and clearer margin, but both fighters were determined and brave, everything their inspiration the legend embodied.
