British light heavyweight Buatsi secured a victory yet unimpressive start to his career under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic medal winner's activity level likely gained him a majority decision in a competitive 10-round bout at the Co-op Live Arena.
But Parker found success, delivering effective individual punches in a fight where the styles didn't complement each other, with constant grabbing disrupting the action.
Two judges judged it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my finest performance but what do champions do? They win," the victor said in the ring as he was met by disapproval from the audience.
The Londoner got back to winning after his first professional defeat - an thrilling contest with Callum Smith in last winter - to secure a 20th pro success.
Several boxing experts felt the challenger, 31, merited the win but the Derbyshire fighter experienced the second defeat of his 28-fight career.
The Champion Claims Win in Uneventful Affair
His career development has slowed in recent years through contract problems and considerable time of inactivity.
Previously predicted as the next star of British boxing, he now stands trying to achieve expectations - maybe in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with the two boxers prepared to take risks in a cagey opening few rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was competing in only his second fight at light heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for the favorite, who operated with a tight guard to barely take the better rounds.
The crowd's patience diminished during frequent holding, with the challenger falling to the floor several times during grappling.
The underdog closed well, but many rounds were difficult to score. Nevertheless, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just one round.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Tribute Motivates Manchester Derby Battle
In the secondary fight, Lyndon Arthur overcame Rea by close verdict in a excellent all-Manchester contest to win the European light-heavyweight title.
The arena became quiet for a extremely emotional tribute prior to the bout as 10 bells sounded in honor of local hero Hatton, who died aged 46 in recently.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the final chime ended, the quiet gave way to a chant of "there's only one Ricky Hatton".
The action within the ring reflected the sentiment. Arthur was sent to the canvas by a significant blow directly to the chin in the early round, rising shakily to his footing on the referee's count.
But the Manchester United-red shorts of Arthur soon advanced again. On the opposite side, the opponent - in rival City blue - was marked up early, noticeable damage developing under his eye as the pair landed powerful shots.
Rea, 27, landed power punches but the champion, 34, responded in kind with effective uppercuts as the action hardly diminished over 12 rounds.
Arthur edged the verdict with judges scorecards of 114-114, 115-113 and clearer margin, but each competitor were persistent and full of heart, everything their hero the legend embodied.
