UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming start to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a split decision in a tight 10-round contest at the Manchester venue.
But Parker found success, delivering effective individual punches in a contest where the styles didn't complement each other, with excessive holding disrupting the contest.
The scoring judges had it 96-94 for to Buatsi, with the third a even score.
"It wasn't my finest display but how do champions respond? They win," Buatsi said in the ring as he was faced boos from the crowd.
The Londoner bounced back after his maiden career setback - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Various analysts thought Parker, 31, should have been awarded the decision but the Derbyshire fighter suffered the second defeat of his 28-fight career.
The Champion Secures Triumph in Dull Affair
His career development has slowed in recent years through management issues and long spells of inactivity.
Earlier forecast as the future of British boxing, he now is positioned trying to realize his potential - maybe in what seems like a ultimate opportunity - under recent support.
He began cautiously, with the two boxers prepared to overcommit in a calculated initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after damaging his hand during the bout, was participating in his second bout at light heavyweight.
By the middle rounds, Parker had kept it close, making life awkward for Buatsi, who utilized a protective stance to edge the more effective stanzas.
The crowd's patience wore thin amid constant clinching, with Parker falling to the floor several times during grappling.
Parker finished the stronger, but multiple periods were hard to judge. However, ex-champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the presence of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Hatton Memorial Inspires Manchester Derby Contest
In the secondary fight, Arthur overcame Bradley Rea by divided decision in a outstanding Manchester vs Manchester contest to capture the European light-heavyweight belt.
The arena grew hushed for a deeply poignant memorial prior to the bout as 10 bells rang in honor of local hero Ricky Hatton, who died at age 46 in last month.
It was the first major televised fight night in the location since Hatton's death. As the concluding sound disappeared, the quiet became a shout of "only one Hatton".
The fighting during the bout matched the feeling. Arthur was knocked down by a left hook squarely on the chin in the initial stage, rising shakily to his position on the eight count.
But the Manchester United-red equipment of Arthur soon came forward again. On the opposite side, Rea - in opposing blue - was marked up quickly, significant bruising developing under his orbital area as the fighters exchanged punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with powerful upward punches as the pace hardly diminished over twelve rounds.
The victor edged the verdict with judges scorecards of 114-114, narrow lead and 115-112, but the two athletes were determined and full of heart, all the qualities their hero the legend embodied.
