British light heavyweight Buatsi secured a victory yet unimpressive debut to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive 10-round bout at the boxing arena.
But Parker had his moments, connecting with powerful clean blows in a match where the techniques failed to mesh, with constant grabbing disrupting the action.
The scoring judges scored it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest showing but how do champions respond? They succeed," the victor stated in the ringside as he was met by 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 last winter - to claim a 20th career victory.
Several boxing experts believed Parker, thirty-one, deserved the victory but the British boxer suffered the second loss of his 28-fight professional journey.
Buatsi Secures Victory in Dull Affair
The fighter's advancement has stalled in recent years through contract problems and extended periods of lack of fights.
Once tipped as the future of British boxing, he now finds himself trying to realize his potential - maybe in what feels like a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors ready to overcommit in a cagey initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was competing in only his second fight at light heavyweight.
By the middle rounds, Parker had made it competitive, creating difficulties for the favorite, who utilized a tight guard to narrowly win the better stanzas.
The crowd's patience diminished during frequent holding, with Parker falling to the floor various instances during close exchanges.
The underdog finished the stronger, but several stanzas were difficult to score. Although, ex-champion Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the caliber of hard hitter Benavidez, and Russian star Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Hatton Homage Fuels Manchester Derby Contest
In the secondary fight, Lyndon Arthur beat Bradley Rea by split-decision in a terrific local rivalry battle to capture the continental title.
The arena became quiet for a profoundly moving homage ahead of the contest as 10 bells rang in remembrance of local hero Ricky Hatton, who died 46 years old in last month.
It was the first major televised fight night in the urban center since the passing of Hatton. As the concluding sound faded, the quiet transitioned to a chant of "there's only one Hatton".
The action during the bout matched the feeling. The eventual winner was knocked down by a powerful punch directly to the chin in the second round, getting up unsteadily to his footing on the referee's count.
But the Manchester United-red attire of the fighter soon advanced again. Across the ring, Rea - in rival City blue - was damaged quickly, heavy swelling developing under his orbital area as the fighters landed hard punches.
Rea, 27, delivered effective strikes but the champion, 34, fought fire with fire with stinging uppercuts as the intensity rarely dropped over twelve rounds.
The victor barely secured the result with scoring tallies of draw, narrow lead and clearer margin, but the two athletes were persistent and full of heart, all the qualities their hero the legend embodied.
