British light heavyweight Buatsi made a winning yet underwhelming beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a competitive 10-round contest at the boxing arena.
But Parker had his moments, landing some telling clean blows in a fight where the approaches didn't complement each other, with frequent clinching spoiling the fight.
Two judges had it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my best performance but what do champions do? They succeed," Buatsi commented in the arena as he was met by negative reactions from the spectators.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in February - to claim a 20th career victory.
Some ringside observers felt Parker, 31, deserved the victory but the British boxer suffered the second loss of his 28-bout professional journey.
Buatsi Secures Win in Slow Match
Buatsi's progress has plateaued in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the future of British boxing, he now stands trying to realize his potential - possibly in what seems like a last chance - under recent support.
He started carefully, with neither fighter prepared to be aggressive in a calculated initial rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in two years ago after suffering a hand injury mid-fight, was making just his second bout at the higher weight class.
By the halfway stage, the underdog had made it competitive, creating difficulties for Buatsi, who worked behind a tight guard to narrowly win the better periods.
The spectators' acceptance wore thin during frequent holding, with the challenger slipping to the canvas several times during grappling.
The underdog closed well, but several stanzas were hard to judge. Nevertheless, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, giving Buatsi just a single round.
The victor advances, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Hatton Memorial Fuels All-Manchester Battle
In the secondary fight, Lyndon Arthur overcame Rea by close verdict in a excellent all-Manchester fight to secure the European light heavyweight belt.
The venue grew hushed for a extremely emotional tribute ahead of the contest as 10 bells tolled in remembrance of local hero Hatton, who died aged 46 in September.
It was the first major televised fight night in the city since the passing of Hatton. As the final chime disappeared, the stillness gave way to a shout of "there's just one Hatton".
The competition inside the ropes reflected the sentiment. The eventual winner was floored by a powerful punch flush on the jaw in the second round, getting up unsteadily to his position on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. Across the ring, the opponent - in opposing blue - was marked up soon, significant bruising appearing under his eye as the pair landed punishing blows.
The challenger, 27, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the pace rarely dropped over the full distance.
Arthur narrowly won the verdict with official scores of draw, 115-113 and wider gap, but both fighters were persistent and courageous, everything their inspiration the legend embodied.
