British light-heavyweight Joshua Buatsi made a winning yet unimpressive start to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a close ten-round bout at the boxing arena.
But Parker had his moments, connecting with powerful clean blows in a contest where the approaches failed to mesh, with constant grabbing disrupting the contest.
The scoring judges judged it 96-94 in favor to the winner, with the third a even score.
"It wasn't my greatest performance but what defines champions? They win," the victor said in the ring as he was met by boos from the audience.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to secure a 20th career victory.
Various analysts thought the challenger, 31, should have been awarded the decision but the Derbyshire fighter suffered the second loss of his 28-fight career.
The Champion Secures Win in Uneventful Encounter
Buatsi's progress has slowed in recent years through management issues and considerable time of inactivity.
Earlier forecast as the next star of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what seems like a ultimate opportunity - under recent support.
He opened tentatively, with the two boxers prepared to overcommit in a tentative early stages.
The challenger, whose only previous defeat came at super middleweight against his former opponent in 2022 after damaging his hand during the bout, was participating in his second appearance at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who operated with a solid defense to narrowly win the more effective stanzas.
The crowd's patience diminished amid regular grabbing, with Parker going down multiple occasions during close exchanges.
Parker finished the stronger, but multiple periods were hard to judge. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
The victor progresses, but with the likes of hard hitter Benavidez, and Russian star Bivol ruling the division, the journey to titles - on this evidence - still appears challenging.
Ricky Hatton Memorial Motivates All-Manchester Fight
In the co-main event, Arthur beat Bradley Rea by divided decision in a excellent local rivalry fight to secure the European light-heavyweight belt.
The arena became quiet for a deeply poignant homage prior to the bout as a bell ceremony rang in remembrance of local hero Hatton, who succumbed aged 46 in last month.
It was the premier televised match card in the urban center since Hatton's death. As the final chime ended, the silence transitioned to a chant of "there's only one Hatton".
The fighting during the bout matched the feeling. The eventual winner was floored by a left hook squarely on the jaw in the initial stage, rising shakily to his position on the eight count.
But the red-colored attire of the fighter soon pressed ahead again. On the opposite side, Rea - in rival City blue - was damaged quickly, noticeable damage forming under his face as the fighters traded powerful shots.
Rea, 27, delivered effective strikes but Arthur, 34, matched the intensity with powerful upward punches as the pace rarely dropped over 12 rounds.
The victor edged the decision with scoring tallies of even score, 115-113 and 115-112, but each competitor were persistent and full of heart, exactly what their hero the legend represented.
