British light-heavyweight Buatsi made a winning yet underwhelming beginning to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a close 10-round fight at the Manchester venue.
But the challenger had his moments, landing some telling clean blows in a contest where the approaches didn't complement each other, with frequent clinching marring the fight.
The scoring judges had it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my finest showing but what defines champions? They succeed," Buatsi stated in the ring as he was met by negative reactions from the spectators.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in February - to earn a 20th career victory.
Some ringside observers thought Parker, 31, deserved the victory but the British boxer experienced the second loss of his 28-bout professional journey.
Buatsi Secures Win in Slow Encounter
Buatsi's progress has stalled in recent times through management issues and considerable time of inactivity.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - maybe in what seems like a final roll of the dice - under recent support.
He started carefully, with neither fighter willing to overcommit in a calculated early stages.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after breaking his hand mid-fight, was making just his second appearance at light-heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for the favorite, who utilized a protective stance to narrowly win the cleaner periods.
The audience's tolerance decreased during constant clinching, with Parker falling to the floor multiple occasions during close exchanges.
The underdog finished the stronger, but many rounds were difficult to score. Nevertheless, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi moves on, but with the caliber of power puncher David Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
Hatton Homage Fuels Local Rivalry Battle
In the secondary fight, Arthur defeated Bradley Rea by split-decision in a terrific local rivalry battle to capture the continental championship.
The stadium fell silent for a extremely emotional memorial prior to the bout as ten bells tolled in remembrance of Manchester's own Ricky Hatton, who passed away aged 46 in September.
It was the first major televised fight night in the city since Hatton's death. As the last bell faded, the quiet became a shout of "there's only one Ricky Hatton".
The fighting inside the ropes equaled the feeling. The eventual winner was floored by a powerful punch flush on the jaw in the second round, rising shakily to his position on the referee's count.
But the Manchester United-red attire of the fighter soon came forward again. On the opposite side, the opponent - in rival City blue - was damaged quickly, heavy swelling developing under his face as the duo traded powerful shots.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with stinging uppercuts as the action seldom decreased over twelve rounds.
The victor edged the decision with official scores of draw, close margin and clearer margin, but the two athletes were relentless and full of heart, everything their idol Hatton represented.
