UK light heavyweight Buatsi made a winning yet underwhelming beginning to life under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a tight 10-round contest at the Co-op Live Arena.
But the challenger found success, connecting with powerful individual punches in a match where the styles failed to mesh, with constant grabbing spoiling the action.
The officials scored it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest performance but how do champions respond? They succeed," the victor stated in the ringside as he was met by disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in February - to earn a 20th career victory.
Several boxing experts believed the challenger, thirty-one, merited the victory but the Derbyshire fighter endured the second loss of his 28-bout professional journey.
The Champion Earns Win in Slow Affair
His career development has stalled in recent years through promotional disputes and long spells of inactivity.
Earlier forecast as the next star of British boxing, he now is positioned trying to realize his potential - maybe in what feels like a final roll of the dice - under recent support.
He started carefully, with the two boxers willing to overcommit in a calculated early stages.
Parker, whose single earlier setback came at super-middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was competing in only his second fight at the higher weight class.
By the middle rounds, Parker had kept it close, causing problems for the favorite, who operated with a tight guard to narrowly win the cleaner rounds.
The spectators' acceptance decreased because of frequent holding, with the challenger slipping to the canvas several times during grappling.
The underdog closed well, but multiple periods were hard to judge. Nevertheless, ex-champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, awarding Buatsi just one round.
Buatsi progresses, but with the likes of heavy hitter Benavidez, and Russian star Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Memorial Motivates Manchester Derby Battle
In the supporting bout, Lyndon Arthur overcame Rea by split-decision in a excellent Manchester vs Manchester battle to secure the European light-heavyweight belt.
The arena grew hushed for a deeply poignant tribute ahead of the contest as 10 bells rang in honor of the city's native Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast boxing event in the urban center since Hatton's passing. As the final chime ended, the quiet transitioned to a shout of "there's just one Hatton".
The action inside the ropes reflected the emotion. Arthur was sent to the canvas by a left hook squarely on the jaw in the initial stage, rising shakily to his position on the referee's count.
But the traditional red equipment of Arthur soon advanced again. On the opposite side, the opponent - in opposing blue - was marked up soon, noticeable damage forming under his orbital area as the fighters landed punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, responded in kind with stinging uppercuts as the intensity rarely dropped over twelve rounds.
The victor barely secured the decision with scoring tallies of draw, 115-113 and clearer margin, but each competitor were persistent and brave, all the qualities their hero Hatton represented.
