UK light-heavyweight Buatsi secured a victory yet unimpressive debut to life under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a competitive ten-round fight at the Manchester venue.
But Parker landed significant shots, connecting with powerful clean blows in a contest where the techniques didn't complement each other, with excessive holding marring the contest.
Two judges had it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest showing but how do champions respond? They prevail," Buatsi said in the ringside as he was greeted with negative reactions from the audience.
The British fighter bounced back after his maiden career setback - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers thought Parker, thirty-one, merited the victory but the Derbyshire fighter suffered the second loss of his 28-bout career.
The Champion Secures Triumph in Dull Encounter
Buatsi's progress has slowed in recent years through promotional disputes and long spells of inactivity.
Once tipped as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with both competitors ready to overcommit in a calculated opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in 2022 after damaging his hand in the contest, was making just his second fight at the higher weight class.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who worked behind a solid defense to edge the more effective rounds.
The spectators' acceptance diminished during regular grabbing, with Parker falling to the floor several times during close exchanges.
Parker finished the stronger, but several stanzas were hard to judge. However, ex-champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
The victor moves on, but with the presence of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Memorial Fuels All-Manchester Contest
In the co-main event, Lyndon Arthur overcame Rea by split-decision in a terrific Manchester vs Manchester fight to capture the continental title.
The venue became quiet for a extremely emotional tribute prior to the bout as a bell ceremony tolled in honor of local hero Hatton, who died at age 46 in recently.
It was the premier televised fight night in the urban center since the passing of Hatton. As the final chime ended, the stillness became a shout of "there's just one Hatton".
The competition inside the ropes equaled the emotion. Arthur was sent to the canvas by a significant blow flush on the jaw in the second round, rising shakily to his footing on the referee's count.
But the red-colored attire of Arthur soon advanced again. Across the ring, Rea - in competitive blue - was marked up early, significant bruising forming under his orbital area as the pair traded powerful shots.
The challenger, 27, landed power punches but the champion, thirty-four, matched the intensity with effective uppercuts as the pace rarely dropped over 12 rounds.
The victor barely secured the decision with judges scorecards of draw, 115-113 and wider gap, but the two athletes were persistent and courageous, exactly what their idol Hatton represented.
