UK light heavyweight Buatsi earned a win yet underwhelming debut to his career under new promoters with a decision win over Zach Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a tight 10-round bout at the Manchester venue.
But Parker landed significant shots, connecting with powerful single shots in a contest where the techniques didn't complement each other, with frequent clinching spoiling the contest.
Two judges judged it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my best showing but how do champions respond? They win," Buatsi said in the ring as he was met by disapproval from the crowd.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in last winter - to earn a twentieth professional win.
Various analysts thought Parker, 31, deserved the decision but the British boxer suffered the second setback of his 28-fight career.
Buatsi Claims Win in Dull Affair
Buatsi's progress has plateaued in recent years through contract problems and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to realize his potential - maybe in what feels like a last chance - under new promotional backing.
He opened tentatively, with neither fighter prepared to overcommit in a calculated early stages.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after damaging his hand during the bout, was participating in his second bout at the higher weight class.
By the fight's midpoint, Parker had made it competitive, causing problems for Buatsi, who worked behind a tight guard to barely take the cleaner stanzas.
The crowd's patience decreased during frequent holding, with Parker going down several times during grappling.
Parker closed well, but multiple periods were hard to judge. However, previous titleholder Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just a single round.
The victor advances, but with the caliber of power puncher David Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Memorial Fuels All-Manchester Contest
In the co-main event, Lyndon Arthur overcame Bradley Rea by split-decision in a excellent local rivalry battle to win the continental belt.
The stadium grew hushed for a deeply poignant memorial ahead of the contest as a bell ceremony sounded in memory of Manchester's own Ricky Hatton, who died at age 46 in recently.
It was the first major televised boxing event in the location since the passing of Hatton. As the final chime ended, the stillness gave way to a roar of "there's just one Hatton".
The competition within the ring reflected the feeling. Arthur was floored by a powerful punch squarely on the face in the second round, rising shakily to his feet on the count of eight.
But the Manchester United-red attire of the fighter soon came forward again. From the other corner, Rea - in rival City blue - was injured early, noticeable damage developing under his eye as the duo exchanged hard punches.
The challenger, 27, landed power punches but Arthur, 34, fought fire with fire with powerful upward punches as the action rarely dropped over twelve rounds.
The victor narrowly won the decision with official scores of even score, close margin and clearer margin, but each competitor were determined and courageous, all the qualities their inspiration Hatton represented.
