UK light heavyweight Buatsi made a winning yet disappointing start to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a competitive ten-round contest at the Co-op Live Arena.
But Parker landed significant shots, delivering effective individual punches in a contest where the styles never quite clicked, with excessive holding spoiling the fight.
The scoring judges scored it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my finest showing but how do champions respond? They succeed," the victor stated in the arena as he was greeted with boos from the crowd.
The Londoner returned to winning ways after his initial pro loss - an epic battle with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts believed Parker, 31, should have been awarded the win but the British boxer endured the second loss of his 28-fight career.
The Champion Claims Win in Dull Encounter
The fighter's advancement has stalled in recent times through promotional disputes and long spells of inactivity.
Once tipped as the future of British boxing, he now is positioned trying to realize his potential - perhaps in what seems like a final roll of the dice - under fresh management.
He began cautiously, with the two boxers ready to be aggressive in a tentative early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand in the contest, was making just his second appearance at the higher weight class.
By the halfway stage, Parker had kept it close, creating difficulties for Buatsi, who operated with a solid defense to narrowly win the more effective rounds.
The audience's tolerance decreased amid frequent holding, with the challenger falling to the floor several times during close exchanges.
Parker closed well, but many rounds were challenging to assess. However, ex-champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the presence of power puncher David Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Homage Motivates Manchester Derby Contest
In the secondary fight, Lyndon Arthur overcame Bradley Rea by divided decision in a terrific all-Manchester contest to capture the European light heavyweight title.
The stadium became quiet for a extremely emotional tribute prior to the bout as ten bells tolled in memory of the city's native Hatton, who succumbed at age 46 in last month.
It was the premier televised boxing event in the city since Hatton's passing. As the last bell disappeared, the silence gave way to a chant of "there's only one Ricky Hatton".
The action within the ring equaled the sentiment. The eventual winner was knocked down by a significant blow squarely on the jaw in the second round, getting up unsteadily to his footing on the referee's count.
But the traditional red shorts of Arthur soon pressed ahead again. Across the ring, the opponent - in competitive blue - was damaged early, heavy swelling developing under his orbital area as the fighters landed hard punches.
The challenger, 27, connected with strong blows but Arthur, 34, matched the intensity with stinging uppercuts as the pace hardly diminished over 12 rounds.
The victor barely secured the decision with official scores of 114-114, 115-113 and clearer margin, but each competitor were persistent and full of heart, everything their idol the legend embodied.
