UK light heavyweight Buatsi earned a win yet underwhelming start to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a majority decision in a close ten-round contest at the Manchester venue.
But Parker had his moments, landing some telling single shots in a match where the techniques never quite clicked, with frequent clinching spoiling the contest.
The officials scored it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest performance but how do champions respond? They succeed," Buatsi commented in the ring as he was met by negative reactions from the spectators.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to secure a 20th career victory.
Some ringside observers thought Parker, thirty-one, should have been awarded the victory but the contender experienced the second setback of his 28-match professional journey.
His career development has slowed in recent times through management issues and extended periods of inactivity.
Previously predicted as the rising talent of British boxing, he now is positioned trying to realize his potential - possibly in what feels like a final roll of the dice - under new promotional backing.
He began cautiously, with both competitors prepared to be aggressive in a tentative initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was competing in only his second fight at light heavyweight.
By the halfway stage, Parker had stayed in contention, making life awkward for Buatsi, who worked behind a tight guard to barely take the more effective periods.
The audience's tolerance wore thin because of regular grabbing, with Parker falling to the floor various instances during close exchanges.
The underdog finished the stronger, but multiple periods were hard to judge. However, former world champion Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the caliber of hard hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
In the supporting bout, Lyndon Arthur beat Rea by close verdict in a terrific Manchester vs Manchester battle to win the European light heavyweight championship.
The venue became quiet for a profoundly moving memorial prior to the bout as ten bells tolled in memory of local hero Hatton, who died 46 years old in recently.
It was the premier televised fight night in the urban center since Hatton's passing. As the final chime faded, the stillness transitioned to a shout of "only one Ricky Hatton".
The action during the bout reflected the emotion. Arthur was sent to the canvas by a powerful punch flush on the jaw in the early round, standing uncertainly to his footing on the eight count.
But the red-colored attire of Arthur soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was marked up early, heavy swelling developing under his orbital area as the fighters landed punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, 34, responded in kind with stinging uppercuts as the intensity rarely dropped over the full distance.
The victor barely secured the decision with judges scorecards of even score, 115-113 and clearer margin, but each competitor were relentless and brave, all the qualities their hero Hatton embodied.
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