British light-heavyweight Buatsi secured a victory yet underwhelming start to life under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a competitive ten-round contest at the Manchester venue.
But the challenger found success, delivering effective clean blows in a contest where the approaches never quite clicked, with excessive holding disrupting the contest.
The officials had it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my finest performance but what defines champions? They succeed," the victor commented in the ringside as he was faced negative reactions from the audience.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in February - to claim a 20th pro success.
Various analysts thought the challenger, thirty-one, should have been awarded the victory but the British boxer endured the second setback of his 28-bout professional journey.
Buatsi Secures Triumph in Slow Encounter
The fighter's advancement has slowed in the past few years through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to fulfil that early promise - maybe in what seems like a last chance - under new promotional backing.
He started carefully, with both competitors ready to overcommit in a tentative opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was competing in only his second bout at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who operated with a solid defense to narrowly win the better rounds.
The crowd's patience decreased during regular grabbing, with Parker falling to the floor various instances during clinches.
The underdog ended stronger, but several stanzas were difficult to score. Although, ex-champion the boxing analyst - working with Dazn - had it significantly in favor for Parker, giving Buatsi just one round.
Buatsi advances, but with the caliber of hard hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Hatton Homage Inspires All-Manchester Fight
In the supporting bout, Lyndon Arthur defeated Bradley Rea by close verdict in a terrific all-Manchester battle to secure the European light-heavyweight belt.
The arena grew hushed for a deeply poignant memorial before the fight as ten bells rang in remembrance of Manchester's own Hatton, who passed away 46 years old in September.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the concluding sound faded, the stillness became a roar of "there's only one Hatton".
The fighting during the bout matched the emotion. The eventual winner was knocked down by a powerful punch squarely on the chin in the second round, rising shakily to his position on the count of eight.
But the Manchester United-red equipment of Arthur soon advanced again. Across the ring, Rea - in opposing blue - was injured early, significant bruising developing under his face as the pair landed hard punches.
The challenger, 27, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the intensity rarely dropped over 12 rounds.
The victor barely secured the decision with judges scorecards of 114-114, narrow lead and wider gap, but each competitor were persistent and full of heart, everything their hero Hatton stood for.
