UK light-heavyweight Buatsi made a winning yet disappointing start to life under new promoters with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a competitive ten-round fight at the boxing arena.
But Parker found success, delivering effective individual punches in a contest where the styles failed to mesh, with excessive holding spoiling the fight.
The officials had it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my best display but how do champions respond? They prevail," the victor commented in the ringside as he was met by negative reactions from the audience.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in last winter - to claim a 20th pro success.
Several boxing experts felt Parker, thirty-one, deserved the victory but the British boxer experienced the second loss of his 28-match professional journey.
The Champion Earns Win in Uneventful Encounter
His career development has stalled in the past few years through contract problems and considerable time of lack of fights.
Once tipped as the next star of the British fight scene, he now stands trying to achieve expectations - possibly in what appears to be a last chance - under new promotional backing.
He started carefully, with the two boxers ready to take risks in a tentative initial rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after suffering a hand injury during the bout, was making just his second appearance at light-heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for the favorite, who utilized a solid defense to barely take the more effective periods.
The spectators' acceptance wore thin amid constant clinching, with Parker going down several times during clinches.
Parker closed well, but several stanzas were hard to judge. However, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the likes of hard hitter David Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Tribute Motivates Local Rivalry Contest
In the co-main event, Lyndon Arthur defeated Bradley Rea by divided decision in a terrific local rivalry fight to secure the European light-heavyweight belt.
The venue became quiet for a deeply poignant tribute before the fight as ten bells rang in honor of the city's native Ricky Hatton, who passed away at age 46 in last month.
It was the first major televised boxing event in the location since Hatton's death. As the final chime ended, the silence gave way to a chant of "only one Ricky Hatton".
The action during the bout reflected the emotion. Arthur was sent to the canvas by a powerful punch flush on the chin in the initial stage, getting up unsteadily to his feet on the count of eight.
But the traditional red shorts of the fighter soon came forward again. From the other corner, Rea - in competitive blue - was damaged soon, significant bruising forming under his orbital area as the pair landed hard punches.
Rea, twenty-seven, landed power punches but the champion, 34, responded in kind with powerful upward punches as the intensity seldom decreased over the full distance.
Arthur narrowly won the verdict with scoring tallies of even score, close margin and wider gap, but each competitor were determined and full of heart, all the qualities their hero Hatton stood for.
