UK light heavyweight Joshua Buatsi made a winning yet disappointing beginning to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a split decision in a competitive ten-round contest at the boxing arena.
But Parker found success, delivering effective clean blows in a match where the approaches failed to mesh, with excessive holding marring the action.
The scoring judges had it 96-94 to the winner, with the final judge a even score.
"It wasn't my greatest display but what defines champions? They prevail," the victor said in the ringside as he was greeted with boos from the audience.
The British fighter got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a 20th career victory.
Several boxing experts felt the challenger, 31, should have been awarded the victory but the contender suffered the second loss of his 28-match professional journey.
Buatsi Claims Win in Slow Encounter
His career development has plateaued in recent years through contract problems and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now is positioned trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors prepared to be aggressive in a cagey opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after damaging his hand mid-fight, was participating in his second appearance at light heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for Buatsi, who utilized a tight guard to barely take the better rounds.
The crowd's patience diminished because of frequent holding, with the challenger going down several times during close exchanges.
The underdog finished the stronger, but many rounds were difficult to score. Although, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the caliber of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Hatton Tribute Fuels Manchester Derby Fight
In the secondary fight, Lyndon Arthur defeated Bradley Rea by divided decision in a excellent all-Manchester battle to secure the European light-heavyweight championship.
The venue grew hushed for a deeply poignant homage before the fight as a bell ceremony tolled in memory of the city's native Ricky Hatton, who died 46 years old in last month.
It was the first major televised fight night in the location since the passing of Hatton. As the last bell faded, the stillness transitioned to a roar of "only one Hatton".
The action during the bout reflected the feeling. Arthur was knocked down by a left hook directly to the chin in the second round, rising shakily to his footing on the referee's count.
But the traditional red shorts of Arthur soon advanced again. Across the ring, the opponent - in opposing blue - was damaged early, noticeable damage forming under his eye as the pair exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with powerful upward punches as the action rarely dropped over the full distance.
Arthur narrowly won the result with judges scorecards of even score, close margin and wider gap, but both fighters were persistent and full of heart, all the qualities their idol the legend represented.
