British light-heavyweight Buatsi made a winning yet disappointing start to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a tight ten-round bout at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective single shots in a match where the styles didn't complement each other, with excessive holding disrupting the contest.
The officials had it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my finest performance but what do champions do? They prevail," Buatsi stated in the arena as he was met by boos from the crowd.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to claim a 20th pro success.
Some ringside observers believed Parker, 31, should have been awarded the victory but the contender suffered the second loss of his 28-fight career.
Buatsi Secures Victory in Dull Encounter
His career development has slowed in the past few years through promotional disputes and considerable time of inactivity.
Previously predicted as the next star of the British fight scene, he now stands trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under recent support.
He began cautiously, with both competitors willing to overcommit in a calculated early stages.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in 2022 after breaking his hand during the bout, was participating in his second fight at the higher weight class.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who operated with a tight guard to edge the better rounds.
The spectators' acceptance diminished amid frequent holding, with the challenger slipping to the canvas various instances during grappling.
The underdog ended stronger, but multiple periods 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.
The victor moves on, but with the caliber of heavy hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Memorial Motivates Local Rivalry Fight
In the supporting bout, Arthur beat Bradley Rea by split-decision in a outstanding Manchester vs Manchester battle to win the European light heavyweight belt.
The stadium became quiet for a deeply poignant homage before the fight as ten bells tolled in memory of Manchester's own Ricky Hatton, who died at age 46 in recently.
It was the initial significant broadcast match card in the location since Hatton's passing. As the final chime disappeared, the silence gave way to a chant of "only one Ricky Hatton".
The competition inside the ropes matched the sentiment. The eventual winner was knocked down by a left hook squarely on the jaw in the early round, rising shakily to his position on the count of eight.
But the red-colored equipment of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was marked up soon, heavy swelling appearing under his eye as the duo traded punishing blows.
The challenger, 27, delivered effective strikes but the champion, 34, fought fire with fire with stinging uppercuts as the intensity hardly diminished over the full distance.
The victor edged the result with judges scorecards of 114-114, close margin and 115-112, but each competitor were determined and full of heart, exactly what their inspiration the legend embodied.
