UK light-heavyweight Buatsi made a winning yet disappointing start to his career under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a split decision in a competitive ten-round bout at the Manchester venue.
But Parker landed significant shots, landing some telling individual punches in a contest where the styles failed to mesh, with frequent clinching marring the contest.
Two judges had it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my best performance but how do champions respond? They win," the victor commented in the ring as he was faced disapproval from the crowd.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in last winter - to earn a twentieth professional win.
Several boxing experts believed the challenger, 31, deserved the decision but the Derbyshire fighter experienced the second defeat of his 28-bout career.
Buatsi Claims Triumph in Dull Affair
The fighter's advancement has plateaued in recent years through management issues and long spells of inactivity.
Previously predicted as the future of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a ultimate opportunity - under new promotional backing.
He opened tentatively, with neither fighter prepared to be aggressive in a cagey early stages.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after damaging his hand in the contest, was making just his second fight at light heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for Buatsi, who utilized a protective stance to barely take the more effective periods.
The crowd's patience wore thin because of constant clinching, with Parker falling to the floor various instances during clinches.
The underdog finished the stronger, but many rounds were challenging to assess. However, previous titleholder the boxing analyst - working with the broadcast network - had it significantly in favor for Parker, awarding Buatsi just a single round.
Buatsi progresses, but with the presence of power puncher David Benavidez, and Russian star Bivol ruling the division, the journey to titles - judging by this showing - still seems difficult.
Hatton Homage Fuels Local Rivalry Battle
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding local rivalry battle to capture the European light heavyweight championship.
The arena grew hushed for a extremely emotional homage before the fight as 10 bells tolled in honor of the city's native Ricky Hatton, who succumbed aged 46 in recently.
It was the first major televised match card in the urban center since Hatton's death. As the final chime ended, the quiet transitioned to a roar of "there's only one Hatton".
The competition inside the ropes matched the feeling. Arthur was floored by a significant blow squarely on the jaw in the initial stage, rising shakily to his feet on the count of eight.
But the red-colored equipment of Arthur soon came forward again. From the other corner, the opponent - in competitive blue - was injured soon, significant bruising developing under his face as the pair landed hard punches.
Rea, 27, delivered effective strikes but Arthur, thirty-four, responded in kind with powerful upward punches as the pace hardly diminished over twelve rounds.
The victor narrowly won the verdict with official scores of 114-114, close margin and 115-112, but both fighters were persistent and full of heart, exactly what their idol Hatton represented.
