British light heavyweight Joshua Buatsi secured a victory yet unimpressive start to life under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a tight ten-round fight at the Co-op Live Arena.
But Parker landed significant shots, delivering effective individual punches in a match where the styles didn't complement each other, with excessive holding spoiling the contest.
The scoring judges scored it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my best display but how do champions respond? They prevail," the victor said in the ring as he was met by disapproval from the crowd.
The Londoner returned to winning ways after his initial pro loss - an epic battle with Callum Smith in last winter - to claim a 20th pro success.
Some ringside observers felt Parker, 31, merited the win but the British boxer experienced the second setback of his 28-bout professional journey.
Buatsi Claims Win in Dull Affair
His career development has plateaued in recent times through management issues and extended periods of inactivity.
Once tipped as the future of British boxing, he now finds himself trying to realize his potential - maybe in what seems like a last chance - under new promotional backing.
He began cautiously, with neither fighter ready to take risks in a calculated opening few rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after breaking his hand in the contest, was competing in only his second appearance at light-heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for Buatsi, who worked behind a solid defense to barely take the better periods.
The crowd's patience wore thin amid frequent holding, with Parker falling to the floor various instances during grappling.
The underdog ended stronger, but many rounds were difficult to score. However, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
The victor advances, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - on this evidence - still appears challenging.
Hatton Memorial Inspires Local Rivalry Battle
In the secondary fight, Lyndon Arthur overcame Bradley Rea by close verdict in a excellent local rivalry fight to win the European light heavyweight title.
The stadium fell silent for a extremely emotional tribute prior to the bout as ten bells sounded in remembrance of Manchester's own Hatton, who died 46 years old in September.
It was the premier televised fight night in the urban center since Hatton's passing. As the concluding sound disappeared, the quiet became a roar of "there's just one Ricky Hatton".
The action during the bout equaled the sentiment. The eventual winner was knocked down by a powerful punch squarely on the jaw in the early round, rising shakily to his feet on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. On the opposite side, Rea - in opposing blue - was injured quickly, noticeable damage developing under his eye as the fighters traded punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, responded in kind with powerful upward punches as the pace hardly diminished over twelve rounds.
Arthur barely secured the verdict with official scores of even score, 115-113 and clearer margin, but each competitor were relentless and full of heart, all the qualities their hero Hatton stood for.
