UK light-heavyweight Joshua Buatsi earned a win yet underwhelming beginning to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a competitive ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful single shots in a fight where the approaches failed to mesh, with constant grabbing spoiling the action.
Two judges had it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best performance but how do champions respond? They win," Buatsi stated in the ringside as he was met by negative reactions from the audience.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to earn a twentieth professional win.
Some ringside observers thought the challenger, thirty-one, merited the win but the Derbyshire fighter suffered the second setback of his 28-fight professional journey.
Buatsi Earns Victory in Slow Match
His career development has plateaued in recent times through contract problems and long spells of lack of fights.
Once tipped as the rising talent of the British fight scene, he now finds himself trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers willing to take risks in a tentative initial rounds.
Parker, whose single earlier setback came at super-middleweight against John Ryder in 2022 after damaging his hand mid-fight, was participating in his second bout at light heavyweight.
By the fight's midpoint, Parker had kept it close, causing problems for Buatsi, who operated with a solid defense to edge the better periods.
The crowd's patience diminished amid constant clinching, with the challenger going down several times during grappling.
Parker finished the stronger, but several stanzas were challenging to assess. Nevertheless, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
Buatsi advances, but with the likes of power puncher Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Memorial Motivates Manchester Derby Fight
In the co-main event, Arthur beat Rea by divided decision in a terrific all-Manchester contest to capture the continental title.
The venue grew hushed for a profoundly moving memorial before the fight as a bell ceremony tolled in memory of local hero Ricky Hatton, who passed away 46 years old in recently.
It was the first major televised boxing event in the urban center since the passing of Hatton. As the last bell disappeared, the silence transitioned to a shout of "only one Hatton".
The action within the ring reflected the sentiment. Arthur was floored by a significant blow directly to the face in the early round, rising shakily to his position on the count of eight.
But the traditional red shorts of Arthur soon came forward again. From the other corner, Rea - in rival City blue - was injured soon, heavy swelling appearing under his orbital area as the pair exchanged punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with effective uppercuts as the pace rarely dropped over 12 rounds.
Arthur edged the verdict with judges scorecards of 114-114, close margin and clearer margin, but both fighters were persistent and courageous, everything their hero the legend embodied.
