UK light heavyweight Joshua Buatsi made a winning yet underwhelming debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a close 10-round bout at the Manchester venue.
But Parker had his moments, delivering effective clean blows in a match where the styles didn't complement each other, with excessive holding spoiling the action.
The scoring judges judged it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest showing but what defines champions? They succeed," Buatsi stated in the ringside as he was met by disapproval from the spectators.
The Londoner bounced back after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Various analysts felt Parker, thirty-one, merited the win but the contender suffered the second defeat of his 28-bout career.
Buatsi Claims Victory in Uneventful Encounter
His career development has stalled in recent years through promotional disputes and long spells of inactivity.
Once tipped as the future of British boxing, he now is positioned trying to realize his potential - maybe in what seems like a final roll of the dice - under fresh management.
He began cautiously, with both competitors willing to be aggressive in a tentative opening few rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after damaging his hand in the contest, was participating in his second bout at light heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a solid defense to edge the cleaner periods.
The crowd's patience diminished because of frequent holding, with the challenger slipping to the canvas various instances during grappling.
Parker ended stronger, but several stanzas were challenging to assess. Nevertheless, former world champion Carl Frampton - commentating on Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
The victor advances, but with the likes of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Tribute Fuels Local Rivalry Contest
In the co-main event, Lyndon Arthur beat Rea by close verdict in a outstanding Manchester vs Manchester battle to capture the European light-heavyweight championship.
The venue grew hushed for a deeply poignant memorial before the fight as a bell ceremony rang in remembrance of the city's native Ricky Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the final chime disappeared, the silence gave way to a roar of "only one Hatton".
The fighting during the bout reflected the sentiment. Arthur was floored by a significant blow squarely on the jaw in the early round, standing uncertainly to his feet on the eight count.
But the traditional red shorts of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was damaged soon, heavy swelling forming under his face as the fighters traded powerful shots.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with powerful upward punches as the action rarely dropped over twelve rounds.
The victor edged the verdict with judges scorecards of 114-114, narrow lead and wider gap, but the two athletes were persistent and brave, everything their hero Hatton embodied.
