UK light heavyweight Joshua Buatsi earned a win yet unimpressive debut to life under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a tight ten-round bout at the Co-op Live Arena.
But Parker found success, connecting with powerful individual punches in a fight where the techniques didn't complement each other, with frequent clinching marring the fight.
Two judges scored it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my greatest performance but what do champions do? They succeed," the victor commented in the ringside as he was met by disapproval from the audience.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Various analysts believed Parker, 31, merited the win but the Derbyshire fighter experienced the second setback of his 28-bout professional journey.
Buatsi Earns Win in Dull Match
The fighter's advancement has plateaued in recent years through contract problems and extended periods of inactivity.
Once tipped as the next star of UK boxing, he now stands trying to realize his potential - perhaps in what feels like a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter ready to be aggressive in a calculated early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after suffering a hand injury in the contest, was competing in only his second fight at light heavyweight.
By the middle rounds, the underdog had stayed in contention, causing problems for the favorite, who operated with a protective stance to barely take the better stanzas.
The spectators' acceptance wore thin during constant clinching, with Parker going down several times during clinches.
The underdog ended stronger, but multiple periods were hard to judge. Although, previous titleholder Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
Buatsi moves on, but with the caliber of hard hitter Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Homage Inspires All-Manchester Contest
In the supporting bout, Arthur beat Bradley Rea by divided decision in a terrific Manchester vs Manchester fight to secure the continental title.
The stadium grew hushed for a extremely emotional memorial prior to the bout as a bell ceremony tolled in honor of the city's native Hatton, who succumbed aged 46 in recently.
It was the premier televised boxing event in the city since Hatton's death. As the final chime ended, the stillness became a roar of "there's only one Hatton".
The action inside the ropes matched the sentiment. The eventual winner was knocked down by a significant blow flush on the face in the early round, rising shakily to his position on the count of eight.
But the Manchester United-red attire of the fighter soon came forward again. From the other corner, Rea - in rival City blue - was injured quickly, significant bruising appearing under his eye as the pair landed punishing blows.
Rea, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with powerful upward punches as the pace seldom decreased over twelve rounds.
The victor edged the result with scoring tallies of even score, close margin and clearer margin, but the two athletes were relentless and brave, all the qualities their hero Hatton stood for.
