UK light heavyweight Joshua Buatsi secured a victory yet unimpressive debut to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a majority decision in a competitive 10-round fight at the Co-op Live Arena.
But the challenger had his moments, landing some telling clean blows in a contest where the techniques never quite clicked, with frequent clinching spoiling the action.
The officials had it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best showing but what do champions do? They succeed," the victor stated in the arena as he was faced negative reactions from the audience.
The Londoner bounced back after his initial pro loss - an thrilling contest with his previous opponent in last winter - to earn a twentieth professional win.
Several boxing experts thought Parker, 31, should have been awarded the decision but the British boxer experienced the second setback of his 28-bout professional journey.
The Champion Claims Victory in Uneventful Encounter
His career development has stalled in recent years through promotional disputes and considerable time of inactivity.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - maybe in what feels like a last chance - under new promotional backing.
He opened tentatively, with the two boxers ready to take risks in a tentative initial rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was making just his second bout at the higher weight class.
By the middle rounds, the underdog had kept it close, making life awkward for the favorite, who worked behind a tight guard to edge the better rounds.
The spectators' acceptance decreased because of frequent holding, with Parker falling to the floor various instances during clinches.
Parker closed well, but multiple periods were difficult to score. Nevertheless, ex-champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
The victor moves on, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Tribute Fuels Local Rivalry Fight
In the secondary fight, Arthur defeated Bradley Rea by split-decision in a terrific local rivalry battle to capture the European light heavyweight title.
The stadium became quiet for a extremely emotional memorial before the fight as a bell ceremony tolled in honor of Manchester's own Ricky Hatton, who succumbed at age 46 in September.
It was the first major televised match card in the location since Hatton's passing. As the final chime ended, the quiet gave way to a roar of "only one Ricky Hatton".
The fighting inside the ropes matched the emotion. The eventual winner was floored by a left hook squarely on the chin in the second round, standing uncertainly to his footing on the count of eight.
But the traditional red shorts of the fighter soon advanced again. On the opposite side, Rea - in rival City blue - was damaged early, heavy swelling appearing under his face as the pair landed hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the action rarely dropped over the full distance.
Arthur edged the result with judges scorecards of even score, close margin and 115-112, but the two athletes were persistent and full of heart, everything their inspiration Hatton stood for.
