British light heavyweight Buatsi secured a victory yet disappointing beginning to life under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a competitive 10-round bout at the Co-op Live Arena.
But Parker had his moments, delivering effective individual punches in a match where the techniques failed to mesh, with frequent clinching marring the contest.
The scoring judges judged it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my best showing but what defines champions? They succeed," the victor stated in the ringside as he was greeted with disapproval from the spectators.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in February - to secure a 20th career victory.
Several boxing experts felt the challenger, 31, merited the victory but the British boxer suffered the second defeat of his 28-match professional journey.
Buatsi Claims Victory in Dull Affair
The fighter's advancement has stalled in recent years through management issues and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under recent support.
He began cautiously, with neither fighter ready to overcommit in a tentative opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for the favorite, who worked behind a protective stance to edge the better rounds.
The spectators' acceptance diminished during regular grabbing, with the challenger falling to the floor various instances during clinches.
The underdog finished the stronger, but many rounds were hard to judge. Nevertheless, previous titleholder the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
Buatsi progresses, but with the likes of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Homage Fuels Local Rivalry Fight
In the supporting bout, Arthur beat Bradley Rea by divided decision in a terrific all-Manchester battle to capture the European light-heavyweight belt.
The arena fell silent for a deeply poignant memorial before the fight as a bell ceremony rang in memory of local hero Ricky Hatton, who succumbed 46 years old in last month.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the final chime disappeared, the silence transitioned to a chant of "there's just one Hatton".
The competition during the bout equaled the emotion. Arthur was sent to the canvas by a powerful punch flush on the face in the early round, rising shakily to his position on the count of eight.
But the red-colored shorts of Arthur soon pressed ahead again. Across the ring, Rea - in rival City blue - was injured quickly, noticeable damage forming under his eye as the duo landed hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with effective uppercuts as the pace rarely dropped over twelve rounds.
Arthur narrowly won the verdict with scoring tallies of 114-114, close margin and 115-112, but each competitor were relentless and courageous, everything their hero Hatton represented.
