UK light-heavyweight Buatsi earned a win yet underwhelming beginning to life under new promoters with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a majority decision in a close ten-round bout at the Co-op Live Arena.
But Parker had his moments, connecting with powerful single shots in a contest where the techniques didn't complement each other, with frequent clinching disrupting the action.
The officials scored it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my greatest showing but what defines champions? They succeed," Buatsi commented in the ring as he was greeted with boos from the spectators.
The Londoner bounced back after his first professional defeat - an epic battle with Callum Smith in last winter - to claim a 20th career victory.
Some ringside observers believed Parker, 31, deserved the decision but the contender suffered the second setback of his 28-match career.
The Champion Secures Triumph in Dull Affair
Buatsi's progress has slowed in the past few years through contract problems and long spells of lack of fights.
Previously predicted as the rising talent of British boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with both competitors prepared to overcommit in a calculated initial rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second bout at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, causing problems for Buatsi, who utilized a protective stance to barely take the cleaner stanzas.
The spectators' acceptance decreased during frequent holding, with the challenger slipping to the canvas several times during clinches.
The underdog finished the stronger, but several stanzas were challenging to assess. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
The victor advances, but with the likes of heavy hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Hatton Homage Inspires Local Rivalry Contest
In the supporting bout, Lyndon Arthur defeated Rea by divided decision in a terrific local rivalry contest to capture the European light heavyweight belt.
The stadium became quiet for a extremely emotional memorial prior to the bout as ten bells sounded in memory of Manchester's own Ricky Hatton, who died aged 46 in last month.
It was the premier televised boxing event in the urban center since Hatton's passing. As the concluding sound faded, the stillness became a shout of "there's only one Hatton".
The competition during the bout matched the sentiment. Arthur was sent to the canvas by a powerful punch squarely on the jaw in the early round, getting up unsteadily to his feet on the referee's count.
But the Manchester United-red equipment of the fighter soon advanced again. Across the ring, Rea - in rival City blue - was damaged soon, significant bruising developing under his face as the fighters traded hard punches.
Rea, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the action hardly diminished over 12 rounds.
Arthur edged the decision with official scores of even score, narrow lead and clearer margin, but each competitor were relentless and courageous, all the qualities their hero Hatton stood for.
