British light heavyweight Joshua Buatsi earned a win yet disappointing debut to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a split decision in a close ten-round fight at the Co-op Live Arena.
But the challenger had his moments, landing some telling individual punches in a match where the approaches didn't complement each other, with constant grabbing disrupting the contest.
The officials scored it 96-94 for to the winner, with the third a 95-95.
"It wasn't my greatest showing but what do champions do? They win," Buatsi commented in the arena as he was faced disapproval from the audience.
The Londoner bounced back after his first professional defeat - an epic battle with Callum Smith in February - to secure a twentieth professional win.
Various analysts thought Parker, 31, should have been awarded the win but the Derbyshire fighter endured the second setback of his 28-fight professional journey.
The Champion Secures Victory in Dull Match
His career development has slowed in the past few years through management issues and long spells of inactivity.
Previously predicted as the rising talent of UK boxing, he now stands trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under recent support.
He started carefully, with both competitors prepared to take risks in a cagey initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury in the contest, was participating in his second appearance at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who worked behind a protective stance to edge the better stanzas.
The crowd's patience decreased amid regular grabbing, with Parker slipping to the canvas various instances during close exchanges.
The underdog finished the stronger, but multiple periods were hard to judge. However, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, giving Buatsi just only one stanza.
The victor advances, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Hatton Tribute Motivates Manchester Derby Contest
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a excellent local rivalry battle to capture the European light heavyweight championship.
The arena grew hushed for a profoundly moving memorial before the fight as a bell ceremony tolled in remembrance of local hero Ricky Hatton, who died 46 years old in September.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the final chime ended, the silence transitioned to a roar of "there's only one Ricky Hatton".
The competition inside the ropes reflected the feeling. The eventual winner was knocked down by a significant blow squarely on the jaw in the early round, standing uncertainly to his feet on the count of eight.
But the red-colored attire of the fighter soon came forward again. On the opposite side, the opponent - in rival City blue - was damaged quickly, heavy swelling developing under his face as the duo traded hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the pace rarely dropped over the full distance.
Arthur barely secured the verdict with official scores of 114-114, narrow lead and clearer margin, but the two athletes were persistent and brave, all the qualities their idol Hatton embodied.
