British light heavyweight Joshua Buatsi earned a win yet unimpressive debut to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a majority decision in a tight ten-round contest at the Manchester venue.
But Parker had his moments, delivering effective single shots in a fight where the styles failed to mesh, with excessive holding marring the fight.
The scoring judges judged it 96-94 for to the winner, with the third a even score.
"It wasn't my best display but how do champions respond? They succeed," Buatsi commented in the ringside as he was met by negative reactions from the crowd.
The Londoner bounced back after his first professional defeat - an epic battle with Callum Smith in February - to secure a 20th career victory.
Several boxing experts believed Parker, 31, deserved the win but the British boxer suffered the second setback of his 28-fight professional journey.
Buatsi Claims Victory in Dull Affair
His career development has plateaued in recent times through management issues and long spells of inactivity.
Earlier forecast as the next star of UK boxing, he now finds himself trying to achieve expectations - maybe in what feels like a last chance - under recent support.
He opened tentatively, with the two boxers ready to overcommit in a tentative opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was participating in his second bout at light heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for the favorite, who worked behind a tight guard to narrowly win the more effective periods.
The audience's tolerance wore thin amid constant clinching, with Parker going down various instances during close exchanges.
The underdog finished the stronger, but several stanzas were difficult to score. Nevertheless, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the presence of power puncher Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Hatton Tribute Motivates Manchester Derby Contest
In the supporting bout, Arthur overcame Bradley Rea by split-decision in a terrific all-Manchester fight to capture the continental title.
The arena fell silent for a deeply poignant homage prior to the bout as ten bells rang in honor of the city's native Hatton, who passed away at age 46 in last month.
It was the first major televised match card in the urban center since Hatton's passing. As the final chime faded, the quiet gave way to a chant of "there's just one Ricky Hatton".
The action during the bout matched the feeling. The eventual winner was floored by a significant blow squarely on the chin in the initial stage, rising shakily to his feet on the eight count.
But the Manchester United-red equipment of the fighter soon came forward again. From the other corner, Rea - in rival City blue - was injured early, heavy swelling developing under his face as the duo landed powerful shots.
Rea, 27, delivered effective strikes but the champion, 34, responded in kind with stinging uppercuts as the pace rarely dropped over the full distance.
The victor narrowly won the decision with official scores of 114-114, close margin and 115-112, but both fighters were relentless and full of heart, exactly what their inspiration the legend stood for.
