UK light-heavyweight Buatsi made a winning yet unimpressive start to his career under new promoters with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a tight ten-round fight at the Manchester venue.
But Parker found success, connecting with powerful individual punches in a contest where the approaches failed to mesh, with excessive holding marring the fight.
The scoring judges had it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my greatest performance but what do champions do? They win," Buatsi commented in the arena as he was greeted with disapproval from the spectators.
The Londoner bounced back after his initial pro loss - an thrilling contest with his previous opponent in last winter - to earn a twentieth professional win.
Various analysts thought the challenger, thirty-one, deserved the win but the British boxer endured the second defeat of his 28-bout career.
Buatsi Earns Win in Uneventful Match
The fighter's advancement has plateaued in recent years through contract problems and considerable time of inactivity.
Once tipped as the rising talent of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with both competitors ready to take risks in a calculated early stages.
Parker, whose single earlier setback came at the lower weight class against John Ryder in 2022 after damaging his hand in the contest, was competing in only his second fight at light heavyweight.
By the middle rounds, Parker had kept it close, making life awkward for Buatsi, who operated with a tight guard to narrowly win the cleaner stanzas.
The audience's tolerance wore thin because of constant clinching, with the challenger slipping to the canvas several times during clinches.
The underdog finished the stronger, but many rounds were hard to judge. Nevertheless, former world champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Memorial Fuels All-Manchester Battle
In the co-main event, Arthur overcame Rea by close verdict in a terrific all-Manchester contest to secure the European light-heavyweight belt.
The arena fell silent for a deeply poignant homage prior to the bout as 10 bells sounded in memory of Manchester's own Hatton, who passed away 46 years old in last month.
It was the first major televised boxing event in the urban center since Hatton's death. As the concluding sound ended, the quiet became a shout of "there's just one Hatton".
The competition within the ring matched the sentiment. The eventual winner was floored by a left hook flush on the face in the early round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red equipment of the fighter soon advanced again. From the other corner, Rea - in competitive blue - was injured soon, heavy swelling forming under his eye as the duo landed punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with effective uppercuts as the pace seldom decreased over twelve rounds.
The victor narrowly won the verdict with official scores of draw, 115-113 and 115-112, but the two athletes were relentless and full of heart, exactly what their idol Hatton represented.
