British light-heavyweight Buatsi secured a victory yet disappointing beginning to his career under fresh promotional backing with a points victory over Zach Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a tight 10-round fight at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful clean blows in a fight where the techniques failed to mesh, with frequent clinching spoiling the action.
The scoring judges scored it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my greatest performance but what defines champions? They win," the victor said in the ring as he was greeted with boos from the crowd.
The Londoner got back to winning after his initial pro loss - an epic battle with Callum Smith in last winter - to earn a twentieth professional win.
Various analysts felt Parker, thirty-one, deserved the victory but the British boxer experienced the second loss of his 28-fight professional journey.
Buatsi Secures Victory in Dull Affair
His career development has stalled in recent times through contract problems and considerable time of inactivity.
Once tipped as the next star of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what seems like a last chance - under recent support.
He began cautiously, with both competitors prepared to be aggressive in a cagey initial rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was making just his second bout at the higher weight class.
By the halfway stage, the underdog had made it competitive, creating difficulties for the favorite, who worked behind a solid defense to barely take the more effective stanzas.
The audience's tolerance decreased during frequent holding, with Parker slipping to the canvas multiple occasions during grappling.
Parker finished the stronger, but many rounds were hard to judge. Although, former world champion Carl Frampton - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Homage Motivates All-Manchester Fight
In the co-main event, Lyndon Arthur beat Rea by close verdict in a terrific all-Manchester contest to secure the European light heavyweight title.
The arena became quiet for a deeply poignant memorial ahead of the contest as ten bells sounded in memory of local hero Ricky Hatton, who succumbed at age 46 in September.
It was the premier televised boxing event in the city since Hatton's death. As the final chime faded, the stillness gave way to a shout of "only one Ricky Hatton".
The competition during the bout equaled the feeling. The eventual winner was sent to the canvas by a powerful punch flush on the jaw in the second round, standing uncertainly to his position on the eight count.
But the traditional red shorts of the fighter soon advanced again. From the other corner, Rea - in rival City blue - was marked up quickly, heavy swelling appearing under his orbital area as the fighters landed hard punches.
Rea, 27, connected with strong blows but Arthur, 34, matched the intensity with effective uppercuts as the intensity hardly diminished over 12 rounds.
The victor narrowly won the verdict with scoring tallies of 114-114, close margin and clearer margin, but both fighters were determined and courageous, all the qualities their hero Hatton stood for.
