UK light heavyweight Buatsi earned a win yet underwhelming debut to life under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a close 10-round bout at the Co-op Live Arena.
But the challenger had his moments, delivering effective individual punches in a contest where the techniques failed to mesh, with excessive holding disrupting the action.
The scoring judges judged it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my best display but how do champions respond? They prevail," Buatsi commented in the ringside as he was faced boos from the audience.
The Londoner bounced back after his first professional defeat - an thrilling contest with Callum Smith in last winter - to secure a 20th pro success.
Some ringside observers believed the challenger, thirty-one, should have been awarded the win but the contender suffered the second loss of his 28-match professional journey.
Buatsi Claims Triumph in Slow Match
The fighter's advancement has stalled in recent years through contract problems and extended periods of inactivity.
Once tipped as the next star of British boxing, he now stands trying to realize his potential - perhaps in what feels like a last chance - under fresh management.
He began cautiously, with both competitors ready to take risks in a calculated opening few rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second fight at light heavyweight.
By the middle rounds, the underdog had made it competitive, making life awkward for the favorite, who utilized a tight guard to edge the more effective stanzas.
The audience's tolerance diminished amid regular grabbing, with Parker going down multiple occasions during grappling.
The underdog finished the stronger, but several stanzas were challenging to assess. Although, former world champion the boxing analyst - commentating on Dazn - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the presence of power puncher David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Hatton Tribute Motivates Manchester Derby Contest
In the supporting bout, Lyndon Arthur defeated Bradley Rea by split-decision in a outstanding Manchester vs Manchester fight to capture the European light heavyweight championship.
The arena fell silent for a extremely emotional memorial prior to the bout as ten bells rang in memory of local hero Hatton, who succumbed 46 years old in recently.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the concluding sound faded, the quiet gave way to a shout of "only one Hatton".
The fighting within the ring matched the feeling. Arthur was sent to the canvas by a powerful punch directly to the chin in the early round, rising shakily to his feet on the eight count.
But the red-colored attire of Arthur soon came forward again. From the other corner, the opponent - in competitive blue - was marked up early, noticeable damage developing under his orbital area as the pair landed hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the pace seldom decreased over twelve rounds.
Arthur barely secured the result with judges scorecards of draw, close margin and clearer margin, but each competitor were persistent and brave, exactly what their idol Hatton embodied.
