UK light heavyweight Joshua Buatsi secured a victory yet underwhelming start to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a close ten-round contest at the Co-op Live Arena.
But Parker had his moments, connecting with powerful single shots in a fight where the techniques never quite clicked, with constant grabbing spoiling the fight.
Two judges judged it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my best display but what defines champions? They prevail," Buatsi said in the ring as he was greeted with disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in February - to secure a 20th pro success.
Some ringside observers believed the challenger, thirty-one, merited the win but the Derbyshire fighter endured the second setback of his 28-bout career.
Buatsi Earns Win in Dull Match
His career development has stalled in recent times through contract problems and extended periods of inactivity.
Once tipped as the next star of the British fight scene, he now finds himself trying to realize his potential - perhaps in what feels like a last chance - under fresh management.
He started carefully, with the two boxers willing to take risks in a calculated early stages.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second appearance at light-heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a protective stance to narrowly win the more effective rounds.
The crowd's patience diminished amid frequent holding, with Parker falling to the floor multiple occasions during clinches.
Parker closed well, but multiple periods were hard to judge. Although, ex-champion the boxing analyst - commentating on Dazn - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor moves on, but with the presence of heavy hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - based on this performance - still seems difficult.
Hatton Tribute Inspires Local Rivalry Fight
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific local rivalry battle to secure the continental championship.
The arena grew hushed for a deeply poignant memorial prior to the bout as ten bells tolled in memory of local hero Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast match card in the city since Hatton's passing. As the concluding sound disappeared, the quiet gave way to a roar of "there's just one Hatton".
The competition during the bout matched the emotion. Arthur was knocked down by a significant blow squarely on the chin in the early round, getting up unsteadily to his position on the eight count.
But the Manchester United-red equipment of Arthur soon advanced again. From the other corner, Rea - in rival City blue - was damaged early, heavy swelling forming under his orbital area as the pair exchanged hard punches.
The challenger, 27, connected with strong blows but Arthur, 34, fought fire with fire with stinging uppercuts as the action hardly diminished over 12 rounds.
The victor edged the decision with scoring tallies of even score, 115-113 and wider gap, but both fighters were relentless and brave, everything their hero the legend represented.
