UK light heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a majority decision in a tight 10-round fight at the Manchester venue.
But Parker found success, delivering effective clean blows in a contest where the approaches never quite clicked, with frequent clinching disrupting the contest.
The scoring judges scored it 96-94 to the winner, with the third a 95-95.
"It wasn't my greatest showing but what defines champions? They prevail," the victor said in the ringside as he was greeted with boos from the spectators.
The British fighter got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a 20th career victory.
Various analysts felt the challenger, 31, should have been awarded the decision but the contender experienced the second loss of his 28-bout career.
Buatsi Earns Triumph in Uneventful Match
Buatsi's progress has stalled in recent years through contract problems and considerable time of inactivity.
Earlier forecast as the rising talent of UK boxing, he now finds himself trying to achieve expectations - maybe in what appears to be a last chance - under new promotional backing.
He started carefully, with the two boxers ready to overcommit in a calculated initial rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in 2022 after damaging his hand in the contest, was participating in his second bout at the higher weight class.
By the fight's midpoint, Parker had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to barely take the cleaner rounds.
The audience's tolerance diminished amid constant clinching, with Parker slipping to the canvas several times during close exchanges.
The underdog closed well, but many rounds were difficult to score. However, ex-champion the boxing analyst - working with Dazn - had it particularly wide for the challenger, giving Buatsi just only one stanza.
Buatsi advances, but with the presence of power puncher Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Tribute Inspires All-Manchester Battle
In the supporting bout, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding local rivalry fight to capture the European light heavyweight belt.
The arena fell silent for a profoundly moving memorial ahead of the contest as ten bells rang in memory of local hero Ricky Hatton, who died at age 46 in September.
It was the initial significant broadcast match card in the location since Hatton's death. As the final chime ended, the quiet gave way to a shout of "there's just one Hatton".
The fighting inside the ropes equaled the sentiment. The eventual winner was sent to the canvas by a powerful punch directly to the jaw in the initial stage, standing uncertainly to his position on the eight count.
But the traditional red attire of Arthur soon advanced again. Across the ring, the opponent - in competitive blue - was marked up soon, heavy swelling forming under his face as the duo exchanged powerful shots.
Rea, 27, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the action seldom decreased over twelve rounds.
Arthur edged the decision with official scores of draw, 115-113 and wider gap, but both fighters were determined and brave, everything their idol Hatton embodied.
