British light-heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a competitive 10-round bout at the boxing arena.
But Parker found success, connecting with powerful individual punches in a fight where the approaches didn't complement each other, with constant grabbing marring the contest.
The scoring judges had it 96-94 for to the winner, with the third a even score.
"It wasn't my finest performance but how do champions respond? They win," the victor said in the arena as he was faced disapproval from the spectators.
The British fighter returned to winning ways after his initial pro loss - an epic battle with Callum Smith in last winter - to secure a 20th career victory.
Various analysts thought Parker, thirty-one, merited the decision but the British boxer endured the second defeat of his 28-fight professional journey.
The Champion Secures Victory in Dull Encounter
The fighter's advancement has plateaued in the past few years through contract problems and considerable time of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to realize his potential - maybe in what appears to be a final roll of the dice - under fresh management.
He started carefully, with neither fighter ready to overcommit in a cagey initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after breaking his hand during the bout, was making just his second fight at the higher weight class.
By the halfway stage, the underdog had made it competitive, creating difficulties for Buatsi, who worked behind a tight guard to narrowly win the better rounds.
The crowd's patience wore thin during regular grabbing, with Parker falling to the floor multiple occasions during grappling.
Parker closed well, but multiple periods were challenging to assess. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Homage Fuels Local Rivalry Contest
In the co-main event, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific local rivalry contest to secure the continental championship.
The venue became quiet for a profoundly moving homage prior to the bout as 10 bells rang in memory of the city's native Hatton, who succumbed 46 years old in September.
It was the first major televised fight night in the urban center since Hatton's passing. As the last bell ended, the silence gave way to a chant of "there's only one Hatton".
The fighting during the bout reflected the sentiment. Arthur was floored by a powerful punch directly to the chin in the second round, rising shakily to his position on the count of eight.
But the Manchester United-red equipment of Arthur soon advanced again. From the other corner, the opponent - in opposing blue - was marked up quickly, heavy swelling developing under his face as the fighters landed punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the pace seldom decreased over twelve rounds.
The victor narrowly won the verdict with judges scorecards of draw, close margin and wider gap, but each competitor were relentless and brave, all the qualities their hero the legend stood for.
