British light-heavyweight Buatsi made a winning yet underwhelming beginning to his career under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a close 10-round bout at the Co-op Live Arena.
But Parker found success, delivering effective individual punches in a match where the styles didn't complement each other, with constant grabbing disrupting the contest.
The officials had it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my finest showing but what do champions do? They prevail," Buatsi stated in the arena as he was greeted with disapproval from the spectators.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in February - to secure a twentieth professional win.
Various analysts thought Parker, thirty-one, merited the victory but the contender endured the second defeat of his 28-bout professional journey.
Buatsi Earns Victory in Slow Match
The fighter's advancement has slowed in recent years through promotional disputes and extended periods of lack of fights.
Once tipped as the next star of UK boxing, he now stands trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under recent support.
He opened tentatively, with neither fighter prepared to be aggressive in a calculated opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after damaging his hand mid-fight, was participating in his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for Buatsi, who worked behind a protective stance to narrowly win the cleaner periods.
The crowd's patience diminished during constant clinching, with Parker falling to the floor multiple occasions during clinches.
The underdog ended stronger, but several stanzas were challenging to assess. However, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Memorial Inspires Manchester Derby Battle
In the co-main event, Lyndon Arthur beat Bradley Rea by close verdict in a excellent all-Manchester contest to win the European light-heavyweight title.
The arena grew hushed for a profoundly moving memorial before the fight as ten bells rang in memory of the city's native Ricky Hatton, who died at age 46 in last month.
It was the first major televised match card in the urban center since the passing of Hatton. As the concluding sound ended, the silence transitioned to a chant of "only one Ricky Hatton".
The action during the bout reflected the feeling. The eventual winner was floored by a left hook directly to the face in the early round, getting up unsteadily to his position on the referee's count.
But the traditional red attire of Arthur soon came forward again. On the opposite side, the opponent - in opposing blue - was injured early, heavy swelling appearing under his orbital area as the pair landed hard punches.
The challenger, 27, delivered effective strikes but Arthur, 34, responded in kind with stinging uppercuts as the intensity rarely dropped over the full distance.
The victor edged the result with official scores of draw, close margin and clearer margin, but each competitor were relentless and brave, everything their hero the legend embodied.
