UK light heavyweight Joshua Buatsi earned a win yet underwhelming debut to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a competitive 10-round fight at the boxing arena.
But the challenger had his moments, delivering effective individual punches in a match where the techniques never quite clicked, with constant grabbing disrupting the fight.
The scoring judges scored it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my best showing but what do champions do? They succeed," the victor said in the ringside as he was faced disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in last winter - to secure a 20th pro success.
Several boxing experts thought Parker, 31, deserved the win but the contender experienced the second setback of his 28-match professional journey.
The Champion Claims Win in Slow Affair
His career development has slowed in recent years through promotional disputes and considerable time of inactivity.
Earlier forecast as the next star of British boxing, he now stands trying to achieve expectations - possibly in what seems like a last chance - under fresh management.
He started carefully, with the two boxers ready to overcommit in a tentative initial rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after breaking his hand mid-fight, was making just his second bout at light-heavyweight.
By the halfway stage, Parker had kept it close, causing problems for Buatsi, who operated with a protective stance to edge the more effective rounds.
The audience's tolerance decreased during regular grabbing, with the challenger falling to the floor multiple occasions during grappling.
The underdog closed well, but multiple periods were hard to judge. Although, former world champion Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
The victor progresses, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Homage Inspires All-Manchester Fight
In the secondary fight, Lyndon Arthur defeated Bradley Rea by close verdict in a outstanding local rivalry contest to win the European light-heavyweight title.
The stadium grew hushed for a profoundly moving tribute ahead of the contest as a bell ceremony tolled in remembrance of local hero Hatton, who passed away at age 46 in last month.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the last bell disappeared, the silence transitioned to a shout of "there's only one Ricky Hatton".
The action within the ring equaled the feeling. The eventual winner was floored by a powerful punch squarely on the face in the initial stage, rising shakily to his footing on the referee's count.
But the traditional red attire of Arthur soon came forward again. From the other corner, the opponent - in rival City blue - was marked up quickly, heavy swelling forming under his face as the pair landed hard punches.
The challenger, 27, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the action rarely dropped over the full distance.
Arthur narrowly won the result with official scores of even score, close margin and wider gap, but both fighters were persistent and full of heart, everything their inspiration the legend embodied.
