British light heavyweight Buatsi made a winning yet underwhelming debut to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a split decision in a competitive ten-round bout at the boxing arena.
But the challenger had his moments, delivering effective individual punches in a fight where the approaches never quite clicked, with constant grabbing spoiling the contest.
Two judges judged it 96-94 for to the winner, with the final judge a even score.
"It wasn't my best showing but how do champions respond? They succeed," the victor stated in the ringside as he was met by disapproval from the spectators.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Several boxing experts thought Parker, 31, merited the victory but the British boxer suffered the second loss of his 28-match career.
The Champion Secures Win in Dull Affair
His career development has slowed in recent years through management issues and long spells of lack of fights.
Once tipped as the next star of the British fight scene, he now stands trying to realize his potential - perhaps in what seems like a final roll of the dice - under recent support.
He started carefully, with both competitors ready to take risks in a calculated initial rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was competing in only his second fight at light heavyweight.
By the middle rounds, Parker had kept it close, making life awkward for the favorite, who worked behind a protective stance to barely take the more effective rounds.
The spectators' acceptance decreased during constant clinching, with Parker falling to the floor several times during close exchanges.
Parker ended stronger, but multiple periods were hard to judge. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
Buatsi advances, but with the likes of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Memorial Fuels Manchester Derby Fight
In the co-main event, Arthur defeated Rea by split-decision in a excellent all-Manchester contest to win the continental title.
The venue fell silent for a profoundly moving tribute before the fight as a bell ceremony tolled in honor of the city's native Hatton, who succumbed aged 46 in last month.
It was the premier televised fight night in the urban center since the passing of Hatton. As the last bell ended, the quiet gave way to a shout of "only one Hatton".
The fighting within the ring matched the feeling. The eventual winner was floored by a left hook squarely on the jaw in the second round, standing uncertainly to his feet on the eight count.
But the red-colored attire of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was marked up early, heavy swelling developing under his face as the pair traded hard punches.
Rea, 27, delivered effective strikes but Arthur, 34, fought fire with fire with powerful upward punches as the pace rarely dropped over the full distance.
The victor narrowly won the verdict with official scores of draw, narrow lead and wider gap, but each competitor were determined and brave, exactly what their inspiration Hatton embodied.
