UK light heavyweight Joshua Buatsi made a winning yet disappointing beginning to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a competitive ten-round fight at the Co-op Live Arena.
But the challenger had his moments, delivering effective single shots in a match where the approaches didn't complement each other, with frequent clinching spoiling the contest.
The scoring judges judged it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my greatest display but how do champions respond? They win," Buatsi said in the ring as he was faced disapproval from the spectators.
The British fighter bounced back after his initial pro loss - an epic battle with his previous opponent in last winter - to secure a 20th pro success.
Several boxing experts thought the challenger, thirty-one, deserved the decision but the contender suffered the second setback of his 28-bout professional journey.
The Champion Earns Win in Slow Affair
Buatsi's progress has plateaued in the past few years through management issues and extended periods of inactivity.
Once tipped as the future of UK boxing, he now stands trying to achieve expectations - maybe in what seems like a last chance - under recent support.
He opened tentatively, with both competitors willing to be aggressive in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after damaging his hand during the bout, was competing in only his second bout at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who worked behind a solid defense to edge the cleaner stanzas.
The audience's tolerance diminished during constant clinching, with the challenger falling to the floor multiple occasions during clinches.
The underdog ended stronger, but multiple periods were difficult to score. Although, former world champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, giving Buatsi just a single round.
The victor moves on, 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 seems difficult.
Hatton Tribute Motivates Manchester Derby Fight
In the co-main event, Arthur overcame Bradley Rea by close verdict in a terrific Manchester vs Manchester fight to secure the European light heavyweight belt.
The arena fell silent for a profoundly moving memorial ahead of the contest as 10 bells tolled in memory of Manchester's own Ricky Hatton, who passed away at age 46 in last month.
It was the first major televised boxing event in the urban center since Hatton's death. As the last bell disappeared, the stillness gave way to a shout of "there's just one Ricky Hatton".
The action during the bout equaled the feeling. The eventual winner was floored by a significant blow flush on the face in the initial stage, standing uncertainly to his position on the referee's count.
But the red-colored equipment of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was marked up early, heavy swelling appearing under his face as the pair exchanged powerful shots.
Rea, twenty-seven, landed power punches but Arthur, 34, responded in kind with powerful upward punches as the intensity hardly diminished over 12 rounds.
Arthur edged the decision with judges scorecards of even score, 115-113 and 115-112, but the two athletes were relentless and courageous, all the qualities their inspiration the legend stood for.
