UK light heavyweight Buatsi made a winning yet disappointing beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a split decision in a competitive ten-round bout at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective single shots in a contest where the techniques never quite clicked, with excessive holding disrupting the fight.
Two judges had it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my best display but what do champions do? They succeed," Buatsi stated in the arena as he was met by disapproval from the audience.
The Londoner got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to secure a 20th career victory.
Various analysts believed the challenger, thirty-one, merited the victory but the Derbyshire fighter endured the second defeat of his 28-fight career.
Buatsi Secures Win in Dull Affair
His career development has plateaued in recent years through promotional disputes and considerable time of lack of fights.
Earlier forecast as the future of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what appears to be a last chance - under recent support.
He started carefully, with neither fighter 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 fight at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who utilized a tight guard to narrowly win the more effective stanzas.
The spectators' acceptance wore thin because of regular grabbing, with Parker falling to the floor various instances during grappling.
The underdog finished the stronger, but several stanzas were hard to judge. However, former world champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the likes of heavy hitter Benavidez, and Russian star Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Hatton Tribute Fuels Local Rivalry Fight
In the co-main event, Lyndon Arthur defeated Bradley Rea by close verdict in a excellent local rivalry battle to capture the European light heavyweight belt.
The arena fell silent for a deeply poignant homage before the fight as 10 bells sounded in memory of the city's native Hatton, who succumbed at age 46 in recently.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the concluding sound faded, the stillness gave way to a roar of "only one Hatton".
The action inside the ropes reflected the sentiment. The eventual winner was knocked down by a significant blow squarely on the face in the initial stage, rising shakily to his position on the eight count.
But the red-colored equipment of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was injured quickly, noticeable damage developing under his face as the fighters traded powerful shots.
The challenger, 27, connected with strong blows but Arthur, 34, matched the intensity with powerful upward punches as the intensity hardly diminished over twelve rounds.
Arthur narrowly won the verdict with scoring tallies of even score, close margin and clearer margin, but the two athletes were relentless and full of heart, everything their idol Hatton stood for.
