UK light heavyweight Buatsi secured a victory yet underwhelming debut to life under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a split decision in a close ten-round bout at the Manchester venue.
But Parker found success, connecting with powerful clean blows in a contest where the approaches failed to mesh, with constant grabbing spoiling the contest.
The officials had it 96-94 for to Buatsi, with the third a even score.
"It wasn't my finest display but how do champions respond? They succeed," the victor commented in the ring as he was greeted with boos from the spectators.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Various analysts thought the challenger, thirty-one, deserved the win but the British boxer endured the second setback of his 28-bout career.
The Champion Secures Triumph in Uneventful Affair
Buatsi's progress has stalled in recent times through management issues and considerable time of lack of fights.
Previously predicted as the future of British boxing, he now stands 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 take risks in a tentative early stages.
Parker, whose single earlier setback came at the lower weight class against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second appearance at light heavyweight.
By the middle rounds, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a tight guard to narrowly win the cleaner rounds.
The audience's tolerance diminished because of regular grabbing, with Parker slipping to the canvas various instances during clinches.
The underdog ended stronger, but several stanzas were difficult to score. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Homage Fuels Local Rivalry Battle
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding all-Manchester fight to win the European light-heavyweight belt.
The stadium fell silent for a deeply poignant homage before the fight as a bell ceremony rang in remembrance of Manchester's own Ricky Hatton, who died aged 46 in last month.
It was the premier televised boxing event in the city since Hatton's death. As the last bell ended, the stillness transitioned to a chant of "there's only one Hatton".
The competition inside the ropes reflected the feeling. Arthur was knocked down by a powerful punch flush on the jaw in the second round, standing uncertainly to his footing on the count of eight.
But the red-colored attire of the fighter soon pressed ahead again. From the other corner, Rea - in rival City blue - was damaged early, heavy swelling forming under his face as the fighters traded hard punches.
The challenger, 27, landed power punches but the champion, thirty-four, responded in kind with stinging uppercuts as the pace hardly diminished over 12 rounds.
The victor narrowly won the decision with judges scorecards of draw, close margin and wider gap, but each competitor were persistent and full of heart, all the qualities their idol the legend stood for.
