UK light heavyweight Buatsi earned a win yet unimpressive beginning to life under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a close 10-round bout at the boxing arena.
But Parker found success, delivering effective single shots in a contest where the approaches failed to mesh, with excessive holding disrupting the action.
Two judges had it 96-94 to the winner, with the remaining official a even score.
"It wasn't my best performance but what do champions do? They prevail," the victor said in the ring as he was faced negative reactions from the crowd.
The British fighter bounced back after his maiden career setback - an epic battle with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers thought Parker, thirty-one, deserved the decision but the contender experienced the second loss of his 28-bout professional journey.
The Champion Claims Win in Slow Affair
His career development has stalled in the past few years through contract problems and considerable time of lack of fights.
Once tipped as the future of UK boxing, he now stands trying to realize his potential - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors prepared to be aggressive in a cagey opening few rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after damaging his hand in the contest, was competing in only his second bout at the higher weight class.
By the middle rounds, the underdog had made it competitive, making life awkward for Buatsi, who utilized a solid defense to barely take the cleaner stanzas.
The crowd's patience decreased amid constant clinching, with Parker going down several times during close exchanges.
The underdog finished the stronger, but multiple periods were hard to judge. However, previous titleholder the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Memorial Motivates All-Manchester Contest
In the secondary fight, Arthur overcame Rea by close verdict in a terrific all-Manchester battle to secure the European light-heavyweight title.
The venue fell silent for a extremely emotional homage ahead of the contest as ten bells sounded in memory of Manchester's own Ricky Hatton, who succumbed 46 years old in September.
It was the first major televised boxing event in the location since Hatton's death. As the last bell faded, the quiet transitioned to a chant of "only one Ricky Hatton".
The fighting within the ring reflected the emotion. The eventual winner was floored by a powerful punch flush on the jaw in the second round, rising shakily to his footing on the eight count.
But the traditional red attire of the fighter soon advanced again. On the opposite side, the opponent - in competitive blue - was damaged early, significant bruising appearing under his orbital area as the pair landed punishing blows.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with effective uppercuts as the pace rarely dropped over 12 rounds.
Arthur edged the verdict with official scores of even score, 115-113 and wider gap, but the two athletes were persistent and brave, everything their inspiration the legend stood for.
