UK light heavyweight Joshua Buatsi earned a win yet underwhelming start to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a split decision in a close ten-round fight at the boxing arena.
But the challenger landed significant shots, landing some telling individual punches in a match where the styles failed to mesh, with excessive holding disrupting the action.
The officials scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my best performance but how do champions respond? They prevail," the victor commented in the ringside as he was greeted with boos from the spectators.
The Londoner got back to winning after his initial pro loss - an epic battle with his previous opponent in February - to earn a 20th pro success.
Several boxing experts thought Parker, thirty-one, deserved the win but the Derbyshire fighter suffered the second loss of his 28-fight professional journey.
The Champion Claims Victory in Slow Match
His career development has slowed in the past few years through contract problems and extended periods of inactivity.
Once tipped as the future of British boxing, he now finds himself trying to fulfil that early promise - possibly in what feels like a last chance - under recent support.
He began cautiously, with both competitors prepared to be aggressive in a cagey initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand in the contest, was making just his second fight at light heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for the favorite, who utilized a protective stance to narrowly win the better rounds.
The spectators' acceptance wore thin because of frequent holding, with Parker slipping to the canvas several times during close exchanges.
The underdog ended stronger, but several stanzas were hard to judge. Nevertheless, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just one round.
Buatsi moves on, but with the presence of hard hitter Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Ricky Hatton Homage Inspires Manchester Derby Battle
In the supporting bout, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding Manchester vs Manchester fight to win the continental championship.
The stadium fell silent for a deeply poignant memorial prior to the bout as a bell ceremony tolled in honor of Manchester's own Ricky Hatton, who succumbed at age 46 in last month.
It was the first major televised boxing event in the city since the passing of Hatton. As the final chime faded, the quiet gave way to a chant of "there's just one Hatton".
The fighting during the bout matched the feeling. The eventual winner was floored by a powerful punch squarely on the face in the early round, rising shakily to his position on the count of eight.
But the red-colored equipment of Arthur soon pressed ahead again. Across the ring, Rea - in competitive blue - was injured soon, noticeable damage forming under his face as the duo traded powerful shots.
Rea, twenty-seven, landed power punches but Arthur, 34, fought fire with fire with effective uppercuts as the action rarely dropped over the full distance.
Arthur narrowly won the decision with official scores of 114-114, close margin and wider gap, but the two athletes were determined and brave, exactly what their idol Hatton represented.
