British light-heavyweight Buatsi made a winning yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a close ten-round fight at the Co-op Live Arena.
But the challenger found success, landing some telling single shots in a match where the styles failed to mesh, with frequent clinching marring the contest.
The scoring judges scored it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my best showing but what do champions do? They succeed," the victor stated in the arena as he was greeted with negative reactions from the spectators.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to earn a twentieth professional win.
Several boxing experts thought the challenger, 31, should have been awarded the win but the Derbyshire fighter experienced the second setback of his 28-match career.
Buatsi Claims Win in Slow Affair
His career development has plateaued in recent years through management issues and long spells of inactivity.
Once tipped as the future of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what appears to be a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors ready to be aggressive in a cagey opening few rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was making just his second appearance at the higher weight class.
By the halfway stage, Parker had stayed in contention, making life awkward for Buatsi, who utilized a tight guard to edge the better stanzas.
The audience's tolerance wore thin because of constant clinching, with Parker going down multiple occasions during clinches.
Parker ended stronger, but several stanzas 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 one round.
The victor moves on, but with the caliber of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Hatton Memorial Inspires Manchester Derby Contest
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a excellent all-Manchester battle to win the continental belt.
The arena fell silent for a deeply poignant memorial ahead of the contest as 10 bells sounded in honor of Manchester's own Hatton, who passed away at age 46 in last month.
It was the premier televised boxing event in the location since Hatton's death. As the last bell faded, the quiet became a shout of "there's only one Ricky Hatton".
The action during the bout matched the emotion. Arthur was floored by a significant blow flush on the jaw in the initial stage, rising shakily to his feet on the eight count.
But the red-colored attire of Arthur soon came forward again. On the opposite side, the opponent - in opposing blue - was damaged soon, significant bruising appearing under his orbital area as the pair traded powerful shots.
Rea, 27, landed power punches but Arthur, 34, fought fire with fire with effective uppercuts as the intensity seldom decreased over twelve rounds.
The victor edged the verdict with official scores of 114-114, narrow lead and clearer margin, but each competitor were persistent and full of heart, all the qualities their hero Hatton embodied.
