UK light heavyweight Buatsi secured a victory yet unimpressive beginning to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a judges' verdict in a tight 10-round fight at the Manchester venue.
But the challenger found success, landing some telling individual punches in a contest where the styles didn't complement each other, with constant grabbing disrupting the action.
The officials had it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They win," Buatsi commented in the ringside as he was greeted with negative reactions from the audience.
The British fighter returned to winning ways after his maiden career setback - an epic battle with his previous opponent in last winter - to earn a 20th pro success.
Some ringside observers thought Parker, 31, deserved the decision but the contender endured the second setback of his 28-fight career.
Buatsi Earns Victory in Slow Match
His career development has slowed in recent years through contract problems and extended periods of lack of fights.
Earlier forecast as the future of the British fight scene, he now stands trying to achieve expectations - possibly in what appears to be a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers ready to be aggressive in a cagey opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after damaging his hand during the bout, was making just his second fight at the higher weight class.
By the halfway stage, the underdog had made it competitive, making life awkward for Buatsi, who worked behind a protective stance to barely take the more effective rounds.
The audience's tolerance decreased amid frequent holding, with the challenger going down several times during grappling.
The underdog finished the stronger, but multiple periods were difficult to score. Nevertheless, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for Parker, awarding Buatsi just only one stanza.
The victor advances, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Memorial Inspires Local Rivalry Fight
In the co-main event, Lyndon Arthur overcame Rea by close verdict in a terrific all-Manchester fight to win the continental belt.
The venue fell silent for a extremely emotional tribute ahead of the contest as ten bells tolled in memory of Manchester's own Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the last bell disappeared, the stillness became a roar of "there's only one Hatton".
The fighting inside the ropes matched the sentiment. The eventual winner was knocked down by a significant blow directly to the chin in the early round, rising shakily to his position on the eight count.
But the traditional red attire of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was injured soon, noticeable damage forming under his eye as the fighters exchanged hard punches.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with effective uppercuts as the pace rarely dropped over twelve rounds.
Arthur barely secured the decision with official scores of even score, close margin and wider gap, but the two athletes were persistent and full of heart, all the qualities their hero Hatton embodied.
