British light-heavyweight Joshua Buatsi secured a victory yet underwhelming debut to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a competitive ten-round bout at the boxing arena.
But Parker landed significant shots, connecting with powerful individual punches in a fight where the styles failed to mesh, with excessive holding disrupting the contest.
The scoring judges had it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest showing but what defines champions? They prevail," Buatsi said in the ring as he was met by boos from the spectators.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to claim a 20th pro success.
Various analysts thought the challenger, 31, should have been awarded the decision but the Derbyshire fighter endured the second loss of his 28-match professional journey.
Buatsi Secures Triumph in Uneventful Affair
His career development has stalled in recent years through management issues and long spells of lack of fights.
Earlier forecast as the future of British boxing, he now is positioned trying to realize his potential - possibly in what appears to be a last chance - under fresh management.
He started carefully, with neither fighter willing to take risks in a cagey initial rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after breaking his hand in the contest, was making just his second fight at the higher weight class.
By the halfway stage, the underdog had stayed in contention, causing problems for the favorite, who utilized a tight guard to narrowly win the more effective stanzas.
The audience's tolerance decreased because of regular grabbing, with the challenger falling to the floor multiple occasions during grappling.
Parker finished the stronger, but multiple periods were challenging to assess. However, previous titleholder Carl Frampton - working with Dazn - had it strongly leaning for Parker, awarding Buatsi just a single round.
Buatsi progresses, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - based on this performance - still appears challenging.
Hatton Tribute Motivates All-Manchester Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a excellent Manchester vs Manchester contest to secure the continental championship.
The arena grew hushed for a profoundly moving homage before the fight as a bell ceremony tolled in remembrance of the city's native Ricky Hatton, who passed away aged 46 in September.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the last bell faded, the stillness gave way to a shout of "there's just one Hatton".
The action during the bout reflected the sentiment. Arthur was floored by a significant blow flush on the face in the early round, getting up unsteadily to his feet on the count of eight.
But the red-colored equipment of the fighter soon pressed ahead again. Across the ring, Rea - in competitive blue - was damaged soon, significant bruising developing under his orbital area as the duo landed punishing blows.
Rea, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with effective uppercuts as the pace seldom decreased over twelve rounds.
Arthur narrowly won the decision with official scores of draw, close margin and clearer margin, but each competitor were determined and brave, exactly what their hero the legend embodied.
