UK light heavyweight Buatsi made a winning yet disappointing debut to his career under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a close ten-round contest at the boxing arena.
But Parker found success, delivering effective single shots in a contest where the approaches didn't complement each other, with frequent clinching marring the fight.
The scoring judges judged it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my finest display but what defines champions? They win," Buatsi stated in the ringside as he was faced negative reactions from the spectators.
The British fighter bounced back after his initial pro loss - an thrilling contest with his previous opponent in last winter - to claim a twentieth professional win.
Various analysts thought Parker, thirty-one, deserved the victory but the contender endured the second defeat of his 28-bout professional journey.
The Champion Earns Victory in Slow Match
The fighter's advancement has slowed in the past few years through management issues and long spells of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now stands trying to realize his potential - possibly in what appears to be a last chance - under fresh management.
He started carefully, with both competitors prepared to overcommit in a cagey opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second fight at light heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for the favorite, who worked behind a solid defense to narrowly win the more effective periods.
The audience's tolerance decreased because of constant clinching, with Parker falling to the floor various instances during grappling.
The underdog finished the stronger, but several stanzas were difficult to score. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Russian star Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Homage Inspires Manchester Derby Fight
In the secondary fight, Arthur beat Rea by divided decision in a outstanding Manchester vs Manchester battle to win the continental title.
The venue became quiet for a profoundly moving tribute before the fight as 10 bells sounded in memory of Manchester's own Ricky Hatton, who died at age 46 in last month.
It was the first major televised fight night in the location since Hatton's death. As the last bell disappeared, the silence gave way to a chant of "there's just one Ricky Hatton".
The competition within the ring equaled the emotion. Arthur was knocked down by a significant blow flush on the chin in the early round, standing uncertainly to his position on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in opposing blue - was injured soon, significant bruising appearing under his orbital area as the duo landed hard punches.
The challenger, 27, connected with strong blows but the champion, 34, responded in kind with powerful upward punches as the action hardly diminished over the full distance.
Arthur narrowly won the verdict with scoring tallies of even score, narrow lead and clearer margin, but both fighters were determined and courageous, all the qualities their hero Hatton represented.
