UK light-heavyweight Joshua Buatsi secured a victory yet unimpressive start to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a judges' verdict in a tight 10-round fight at the Co-op Live Arena.
But Parker found success, delivering effective single shots in a fight where the approaches never quite clicked, with excessive holding disrupting the contest.
Two judges judged it 96-94 for to the winner, with the third a 95-95.
"It wasn't my finest performance but what do champions do? They prevail," Buatsi commented in the ringside as he was faced boos from the crowd.
The British fighter bounced back after his initial pro loss - an thrilling contest with his previous opponent in last winter - to claim a 20th career victory.
Several boxing experts believed Parker, 31, should have been awarded the victory but the British boxer endured the second defeat of his 28-bout professional journey.
The Champion Secures Victory in Slow Encounter
His career development has slowed in the past few years through promotional disputes and extended periods of inactivity.
Previously predicted as the next star of the British fight scene, he now stands trying to achieve expectations - maybe in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers ready to overcommit in a tentative early stages.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was participating in his second appearance at light heavyweight.
By the halfway stage, the underdog had made it competitive, making life awkward for Buatsi, who utilized a tight guard to narrowly win the cleaner rounds.
The crowd's patience wore thin during regular grabbing, with the challenger falling to the floor several times during grappling.
Parker closed well, but multiple periods were hard to judge. Nevertheless, previous titleholder Carl Frampton - working with Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
The victor moves on, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Memorial Inspires All-Manchester Battle
In the supporting bout, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding local rivalry contest to capture the European light heavyweight championship.
The arena grew hushed for a deeply poignant tribute before the fight as ten bells sounded in memory of local hero Hatton, who died at age 46 in recently.
It was the first major televised match card in the location since Hatton's death. As the last bell faded, the stillness gave way to a chant of "there's just one Hatton".
The action within the ring matched the feeling. The eventual winner was floored by a significant blow flush on the jaw in the initial stage, rising shakily to his footing on the count of eight.
But the traditional red equipment of the fighter soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was marked up early, noticeable damage forming under his orbital area as the pair traded punishing blows.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the pace seldom decreased over twelve rounds.
The victor barely secured the verdict with judges scorecards of draw, narrow lead and 115-112, but each competitor were determined and courageous, exactly what their inspiration Hatton represented.
