UK light-heavyweight Buatsi secured a victory yet underwhelming debut to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a majority decision in a tight 10-round contest at the boxing arena.
But the challenger found success, connecting with powerful single shots in a contest where the approaches never quite clicked, with frequent clinching marring the fight.
Two judges had it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest display but what defines champions? They prevail," the victor 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 memorable fight with his previous opponent in February - to secure a 20th career victory.
Some ringside observers believed Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter endured the second setback of his 28-bout professional journey.
Buatsi Earns Win in Dull Encounter
Buatsi's progress has stalled in recent times through promotional disputes and considerable time of inactivity.
Previously predicted as the rising talent of the British fight scene, he now stands trying to fulfil that early promise - perhaps in what seems like a last chance - under recent support.
He opened tentatively, with neither fighter willing to take risks in a tentative opening few rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, making life awkward for the favorite, who worked behind a protective stance to narrowly win the better periods.
The spectators' acceptance wore thin amid constant clinching, with the challenger slipping to the canvas several times during grappling.
Parker ended stronger, but many rounds were challenging to assess. However, previous titleholder Carl Frampton - working with Dazn - had it particularly wide for the challenger, awarding Buatsi just one round.
Buatsi advances, but with the likes of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
Hatton Homage Fuels Local Rivalry Contest
In the supporting bout, Lyndon Arthur beat Rea by split-decision in a terrific Manchester vs Manchester battle to secure the continental championship.
The stadium became quiet for a extremely emotional memorial before the fight as a bell ceremony tolled in remembrance of Manchester's own Hatton, who succumbed 46 years old in last month.
It was the premier televised boxing event in the urban center since Hatton's passing. As the concluding sound faded, the quiet transitioned to a chant of "only one Ricky Hatton".
The competition during the bout matched the sentiment. Arthur was knocked down by a left hook squarely on the chin in the second round, standing uncertainly to his feet on the count of eight.
But the Manchester United-red attire of the fighter soon advanced again. Across the ring, the opponent - in opposing blue - was damaged quickly, significant bruising forming under his face as the pair landed punishing blows.
The challenger, 27, connected with strong blows but Arthur, 34, fought fire with fire with stinging uppercuts as the action hardly diminished over the full distance.
The victor barely secured the verdict with scoring tallies of 114-114, close margin and 115-112, but the two athletes were persistent and courageous, all the qualities their inspiration Hatton stood for.
