British light heavyweight Joshua Buatsi secured a victory yet unimpressive start to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a majority decision in a tight ten-round contest at the Manchester venue.
But Parker found success, connecting with powerful clean blows in a match where the techniques didn't complement each other, with frequent clinching marring the action.
The officials had it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my finest performance but what do champions do? They succeed," Buatsi stated in the ringside as he was greeted with boos from the crowd.
The Londoner bounced back after his first professional defeat - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Some ringside observers thought Parker, 31, deserved the decision but the contender endured the second loss of his 28-fight professional journey.
Buatsi Earns Victory in Dull Encounter
The fighter's advancement has slowed in the past few years through promotional disputes and long spells of lack of fights.
Earlier forecast as the next star of UK boxing, he now finds himself trying to achieve expectations - perhaps in what appears to be a last chance - under recent support.
He opened tentatively, with the two boxers prepared to be aggressive in a tentative initial rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in 2022 after damaging his hand mid-fight, was participating in his second appearance at the higher weight class.
By the halfway stage, Parker had stayed in contention, causing problems for the favorite, who worked behind a tight guard to edge the cleaner rounds.
The spectators' acceptance diminished amid frequent holding, with the challenger slipping to the canvas multiple occasions during clinches.
Parker closed well, but several stanzas were challenging to assess. Nevertheless, former world champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor advances, but with the caliber of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - based on this performance - still appears challenging.
Hatton Tribute Inspires Local Rivalry Fight
In the supporting bout, Lyndon Arthur beat Rea by split-decision in a terrific all-Manchester fight to capture the European light-heavyweight belt.
The stadium grew hushed for a profoundly moving memorial ahead of the contest as 10 bells sounded in memory of local hero Ricky Hatton, who passed away aged 46 in recently.
It was the premier televised boxing event in the city since Hatton's death. As the final chime ended, the silence gave way to a shout of "there's just one Hatton".
The fighting within the ring equaled the feeling. Arthur was knocked down by a powerful punch directly to the jaw in the second round, getting up unsteadily to his position on the referee's count.
But the Manchester United-red attire of Arthur soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was damaged soon, noticeable damage developing under his orbital area as the fighters traded hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with powerful upward punches as the intensity rarely dropped over twelve rounds.
The victor barely secured the result with official scores of draw, close margin and clearer margin, but each competitor were determined and brave, all the qualities their hero Hatton represented.
