UK light-heavyweight Buatsi made a winning yet underwhelming start to life under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a majority decision in a close 10-round bout at the Manchester venue.
But Parker landed significant shots, landing some telling single shots in a contest where the approaches didn't complement each other, with constant grabbing spoiling the fight.
The officials had it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my greatest showing but what defines champions? They prevail," Buatsi commented in the ring as he was met by negative reactions from the crowd.
The British fighter returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to claim a 20th career victory.
Some ringside observers felt Parker, 31, merited the victory but the Derbyshire fighter suffered the second setback of his 28-match professional journey.
The Champion Earns Triumph in Uneventful Encounter
His career development has stalled in recent times through contract problems and considerable time of lack of fights.
Once tipped as the next star of UK boxing, he now finds himself trying to realize his potential - maybe in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors ready to overcommit in a cagey opening few rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was competing in only his second bout at the higher weight class.
By the middle rounds, Parker had made it competitive, making life awkward for Buatsi, who worked behind a solid defense to narrowly win the cleaner periods.
The audience's tolerance diminished because of constant clinching, with the challenger slipping to the canvas several times during close exchanges.
The underdog finished the stronger, but many rounds were difficult to score. Although, ex-champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still appears challenging.
Hatton Memorial Inspires All-Manchester Battle
In the supporting bout, Arthur overcame Bradley Rea by split-decision in a excellent Manchester vs Manchester fight to capture the continental title.
The venue fell silent for a extremely emotional tribute before the fight as a bell ceremony sounded in honor of Manchester's own Ricky Hatton, who succumbed aged 46 in last month.
It was the first major televised boxing event in the urban center since Hatton's death. As the final chime disappeared, the stillness transitioned to a shout of "only one Ricky Hatton".
The competition inside the ropes equaled the sentiment. Arthur was floored by a powerful punch flush on the jaw in the early round, standing uncertainly to his footing on the count of eight.
But the traditional red attire of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was injured quickly, heavy swelling appearing under his face as the pair landed powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with effective uppercuts as the pace rarely dropped over twelve rounds.
The victor narrowly won the verdict with scoring tallies of 114-114, close margin and 115-112, but both fighters were persistent and brave, exactly what their hero Hatton stood for.
