British light heavyweight Joshua Buatsi earned a win yet unimpressive beginning to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a split decision in a competitive ten-round contest at the Co-op Live Arena.
But Parker had his moments, landing some telling clean blows in a contest where the techniques didn't complement each other, with frequent clinching marring the fight.
Two judges judged it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my best display but how do champions respond? They succeed," the victor commented in the ringside as he was met by disapproval from the audience.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to secure a 20th pro success.
Several boxing experts thought Parker, thirty-one, should have been awarded the win but the Derbyshire fighter experienced the second defeat of his 28-match career.
Buatsi Secures Win in Dull Affair
The fighter's advancement has stalled in recent years through promotional disputes and long spells of inactivity.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to realize his potential - maybe in what seems like a last chance - under fresh management.
He started carefully, with the two boxers prepared to overcommit in a calculated initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after damaging his hand mid-fight, was making just his second fight at light heavyweight.
By the halfway stage, Parker had kept it close, causing problems for Buatsi, who worked behind a tight guard to barely take the more effective stanzas.
The crowd's patience diminished during frequent holding, with the challenger slipping to the canvas multiple occasions during clinches.
The underdog finished the stronger, but many rounds were challenging to assess. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the presence of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Motivates All-Manchester Fight
In the co-main event, Arthur overcame Rea by close verdict in a outstanding local rivalry fight to capture the European light heavyweight belt.
The venue fell silent for a extremely emotional tribute ahead of the contest as 10 bells rang in memory of local hero Ricky Hatton, who passed away at age 46 in recently.
It was the premier televised boxing event in the city since Hatton's passing. As the final chime disappeared, the silence gave way to a shout of "there's only one Hatton".
The action during the bout reflected the feeling. Arthur was knocked down by a left hook flush on the chin in the initial stage, standing uncertainly to his feet on the referee's count.
But the Manchester United-red attire of Arthur soon advanced again. From the other corner, Rea - in rival City blue - was marked up quickly, significant bruising developing under his orbital area as the duo exchanged punishing blows.
Rea, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with effective uppercuts as the action rarely dropped over 12 rounds.
Arthur edged the verdict with judges scorecards of even score, narrow lead and 115-112, but both fighters were relentless and full of heart, all the qualities their hero the legend represented.
