UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming start to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a judges' verdict in a competitive 10-round fight at the Manchester venue.
But the challenger had his moments, connecting with powerful individual punches in a match where the styles didn't complement each other, with constant grabbing marring the fight.
The scoring judges judged it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my best showing but what do champions do? They prevail," Buatsi stated in the arena as he was greeted with negative reactions from the audience.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Various analysts thought Parker, thirty-one, deserved the victory but the contender suffered the second loss of his 28-fight professional journey.
The Champion Secures Triumph in Uneventful Encounter
The fighter's advancement has stalled in recent times through contract problems and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now is positioned trying to achieve expectations - maybe in what appears to be a last chance - under new promotional backing.
He started carefully, with both competitors prepared to overcommit in a tentative early stages.
Parker, whose sole prior loss came at the lower weight class against John Ryder in 2022 after breaking his hand in the contest, was making just his second appearance at light heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for the favorite, who utilized a solid defense to narrowly win the more effective stanzas.
The audience's tolerance diminished because of regular grabbing, with the challenger slipping to the canvas multiple occasions during clinches.
The underdog closed well, but many rounds were hard to judge. However, former world champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, awarding Buatsi just one round.
The victor progresses, but with the presence of power puncher Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Tribute Inspires All-Manchester Battle
In the secondary fight, Lyndon Arthur overcame Rea by divided decision in a outstanding all-Manchester contest to win the continental title.
The arena grew hushed for a extremely emotional memorial prior to the bout as 10 bells rang in honor of Manchester's own Hatton, who passed away at age 46 in recently.
It was the first major televised boxing event in the location since the passing of Hatton. As the final chime ended, the quiet gave way to a roar of "there's just one Hatton".
The action within the ring equaled the feeling. The eventual winner was knocked down by a left hook directly to the face in the second round, standing uncertainly to his position on the referee's count.
But the red-colored equipment of Arthur soon came forward again. On the opposite side, Rea - in competitive blue - was injured early, heavy swelling developing under his eye as the fighters exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with powerful upward punches as the intensity rarely dropped over twelve rounds.
The victor edged the decision with scoring tallies of even score, narrow lead and 115-112, but the two athletes were relentless and courageous, exactly what their inspiration the legend represented.
