British light-heavyweight Joshua Buatsi earned a win yet underwhelming start to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive 10-round bout at the Manchester venue.
But the challenger landed significant shots, delivering effective single shots in a contest where the techniques never quite clicked, with constant grabbing marring the action.
The officials judged it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my finest display but what defines champions? They win," the victor stated in the ringside as he was faced boos from the crowd.
The Londoner returned to winning ways after his maiden career setback - an epic battle with his previous opponent in last winter - to claim a twentieth professional win.
Some ringside observers believed Parker, 31, deserved the win but the contender experienced the second setback of his 28-fight professional journey.
Buatsi Secures Victory in Uneventful Encounter
His career development has slowed in the past few years through promotional disputes and extended periods of inactivity.
Earlier forecast as the next star of British boxing, he now is positioned trying to achieve expectations - possibly in what feels like a ultimate opportunity - under recent support.
He started carefully, with neither fighter ready to be aggressive in a calculated initial rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand mid-fight, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, causing problems for the favorite, who utilized a solid defense to barely take the cleaner stanzas.
The audience's tolerance wore thin amid constant clinching, with the challenger falling to the floor various instances during clinches.
The underdog closed well, but multiple periods were difficult to score. Although, previous titleholder Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just a single round.
The victor progresses, but with the likes of power puncher Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Homage Inspires All-Manchester Contest
In the supporting bout, Lyndon Arthur overcame Bradley Rea by divided decision in a terrific all-Manchester fight to win the European light heavyweight belt.
The venue grew hushed for a deeply poignant homage prior to the bout as ten bells rang in remembrance of the city's native Ricky Hatton, who succumbed 46 years old in recently.
It was the premier televised match card in the urban center since Hatton's death. As the final chime faded, the stillness transitioned to a roar of "only one Hatton".
The competition inside the ropes matched the feeling. Arthur was floored by a left hook flush on the face in the early round, standing uncertainly to his position on the referee's count.
But the red-colored attire of Arthur soon came forward again. From the other corner, the opponent - in competitive blue - was injured soon, significant bruising developing under his face as the fighters traded punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the pace rarely dropped over twelve rounds.
Arthur barely secured the verdict with official scores of even score, narrow lead and wider gap, but each competitor were persistent and brave, everything their hero Hatton represented.
