UK light-heavyweight Buatsi made a winning yet underwhelming start to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a competitive ten-round contest at the Manchester venue.
But Parker had his moments, connecting with powerful single shots in a contest where the techniques never quite clicked, with constant grabbing spoiling the fight.
Two judges scored it 96-94 for to the winner, with the third a 95-95.
"It wasn't my finest display but how do champions respond? They prevail," the victor stated in the ring as he was faced boos from the crowd.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in February - to claim a 20th career victory.
Some ringside observers felt the challenger, thirty-one, deserved the victory but the British boxer experienced the second loss of his 28-match professional journey.
The Champion Secures Win in Uneventful Affair
The fighter's advancement has stalled in recent times through management issues and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to achieve expectations - possibly in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers prepared to take risks in a cagey initial rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after breaking his hand during the bout, was participating in his second fight at light heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for Buatsi, who operated with a protective stance to barely take the more effective stanzas.
The spectators' acceptance wore thin during regular grabbing, with Parker going down several times during clinches.
The underdog finished the stronger, but several stanzas were difficult to score. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
The victor progresses, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Memorial Fuels Manchester Derby Contest
In the secondary fight, Lyndon Arthur beat Rea by split-decision in a excellent local rivalry battle to win the continental championship.
The venue fell silent for a deeply poignant homage prior to the bout as ten bells rang in remembrance of the city's native Ricky Hatton, who passed away at age 46 in recently.
It was the first major televised boxing event in the city since the passing of Hatton. As the last bell disappeared, the stillness became a chant of "only one Ricky Hatton".
The competition within the ring reflected the emotion. The eventual winner was knocked down by a significant blow directly to the face in the early round, standing uncertainly to his position on the referee's count.
But the traditional red equipment of Arthur soon advanced again. On the opposite side, Rea - in opposing blue - was injured early, significant bruising appearing under his face as the duo traded hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with stinging uppercuts as the action seldom decreased over twelve rounds.
Arthur barely secured the verdict with official scores of 114-114, narrow lead and 115-112, but the two athletes were persistent and brave, everything their idol the legend embodied.
