British light heavyweight Buatsi secured a victory yet unimpressive start to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive ten-round bout at the Co-op Live Arena.
But Parker had his moments, delivering effective clean blows in a contest where the techniques failed to mesh, with excessive holding spoiling the contest.
The scoring judges judged it 96-94 to Buatsi, with the third a even score.
"It wasn't my best showing but what do champions do? They prevail," Buatsi commented in the arena as he was met by disapproval from the crowd.
The British fighter got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Various analysts believed the challenger, 31, should have been awarded the decision but the Derbyshire fighter endured the second loss of his 28-match career.
The Champion Secures Victory in Dull Affair
Buatsi's progress has plateaued in recent times through promotional disputes and extended periods of lack of fights.
Once tipped as the rising talent of UK boxing, he now stands trying to realize his potential - possibly in what seems like a last chance - under recent support.
He began cautiously, with the two boxers willing to be aggressive in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second fight at light-heavyweight.
By the middle rounds, Parker had stayed in contention, causing problems for Buatsi, who operated with a protective stance to edge the better rounds.
The crowd's patience diminished amid constant clinching, with the challenger slipping to the canvas several times during grappling.
Parker finished the stronger, but many rounds were difficult to score. Although, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just a single round.
Buatsi moves on, but with the caliber of hard hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Hatton Tribute Motivates Manchester Derby Contest
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a excellent Manchester vs Manchester contest to win the European light heavyweight championship.
The venue fell silent for a profoundly moving tribute prior to the bout as a bell ceremony sounded in remembrance of the city's native 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 faded, the stillness gave way to a shout of "there's only one Hatton".
The fighting inside the ropes matched the sentiment. The eventual winner was floored by a left hook flush on the chin in the early round, rising shakily to his feet on the eight count.
But the Manchester United-red shorts of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was injured quickly, noticeable damage appearing under his eye as the duo landed powerful shots.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, responded in kind with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur edged the decision with judges scorecards of 114-114, close margin and clearer margin, but each competitor were persistent and courageous, exactly what their idol Hatton stood for.
