UK light-heavyweight Buatsi earned a win yet disappointing debut to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a tight ten-round bout at the boxing arena.
But Parker landed significant shots, delivering effective single shots in a contest where the techniques never quite clicked, with constant grabbing marring the contest.
The scoring judges judged it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my finest display but how do champions respond? They win," the victor stated in the arena as he was faced disapproval from the spectators.
The Londoner bounced back after his first professional defeat - an memorable fight with Callum Smith in February - to earn a 20th pro success.
Several boxing experts believed the challenger, thirty-one, deserved the victory but the Derbyshire fighter suffered the second setback of his 28-bout career.
Buatsi Secures Triumph in Dull Affair
The fighter's advancement has stalled in recent times through contract problems and considerable time of inactivity.
Once tipped as the next star of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a last chance - under fresh management.
He began cautiously, with the two boxers willing to overcommit in a calculated early stages.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after suffering a hand injury during the bout, was participating in his second appearance at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to narrowly win the cleaner rounds.
The audience's tolerance diminished during constant clinching, with Parker falling to the floor multiple occasions during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. Nevertheless, ex-champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Hatton Memorial Motivates Local Rivalry Battle
In the secondary fight, Arthur beat Rea by divided decision in a outstanding local rivalry battle to secure the continental championship.
The stadium fell silent for a profoundly moving tribute ahead of the contest as ten bells tolled in honor of the city's native Ricky Hatton, who succumbed 46 years old in last month.
It was the premier televised boxing event in the urban center since Hatton's death. As the final chime faded, the silence became a shout of "there's just one Ricky Hatton".
The competition within the ring equaled the emotion. Arthur was sent to the canvas by a powerful punch flush on the jaw in the early round, rising shakily to his feet on the referee's count.
But the Manchester United-red attire of the fighter soon came forward again. On the opposite side, Rea - in rival City blue - was marked up soon, significant bruising developing under his face as the fighters traded powerful shots.
Rea, 27, landed power punches but the champion, 34, matched the intensity with powerful upward punches as the pace hardly diminished over the full distance.
The victor barely secured the result with official scores of 114-114, narrow lead and clearer margin, but the two athletes were relentless and full of heart, everything their hero Hatton stood for.
