British light heavyweight Joshua Buatsi made a winning yet underwhelming start to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a tight 10-round bout at the boxing arena.
But Parker found success, connecting with powerful clean blows in a match where the approaches didn't complement each other, with excessive holding spoiling the contest.
Two judges had it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my finest display but what defines champions? They prevail," Buatsi stated in the ring as he was faced boos from the spectators.
The Londoner bounced back after his maiden career setback - an epic battle with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, should have been awarded the decision but the British boxer endured the second setback of his 28-bout professional journey.
The Champion Secures Triumph in Dull Match
His career development has stalled in the past few years through contract problems and considerable time of inactivity.
Once tipped as the next star of British boxing, he now stands trying to achieve expectations - maybe in what appears to be a last chance - under new promotional backing.
He started carefully, with the two boxers willing to be aggressive in a calculated opening few rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was competing in only his second appearance at light-heavyweight.
By the halfway stage, Parker had made it competitive, creating difficulties for Buatsi, who operated with a protective stance to edge the better rounds.
The audience's tolerance diminished because of constant clinching, with the challenger going down multiple occasions during clinches.
The underdog finished the stronger, but multiple periods were difficult to score. Nevertheless, previous titleholder Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi advances, but with the likes of power puncher Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - on this evidence - still seems difficult.
Hatton Homage Inspires Manchester Derby Battle
In the co-main event, Arthur overcame Bradley Rea by divided decision in a excellent Manchester vs Manchester battle to capture the continental belt.
The stadium fell silent for a profoundly moving homage before the fight as 10 bells tolled in honor of Manchester's own Hatton, who died 46 years old in September.
It was the first major televised match card in the location since Hatton's death. As the last bell faded, the quiet transitioned to a shout of "there's only one Ricky Hatton".
The fighting inside the ropes reflected the feeling. Arthur was floored by a significant blow directly to the chin in the early round, getting up unsteadily to his position on the count of eight.
But the traditional red attire of Arthur soon came forward again. On the opposite side, the opponent - in competitive blue - was marked up quickly, significant bruising forming under his face as the duo traded powerful shots.
The challenger, 27, delivered effective strikes but the champion, 34, matched the intensity with effective uppercuts as the intensity hardly diminished over twelve rounds.
Arthur edged the result with judges scorecards of 114-114, close margin and 115-112, but both fighters were determined and courageous, everything their inspiration the legend embodied.
