British light-heavyweight Buatsi earned a win yet underwhelming beginning to life under new promoters 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 ten-round fight at the Manchester venue.
But the challenger found success, landing some telling single shots in a match where the approaches failed to mesh, with excessive holding disrupting the fight.
The officials judged it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my finest performance but how do champions respond? They succeed," the victor commented in the arena as he was met by negative reactions from the audience.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in last winter - to claim a 20th career victory.
Several boxing experts believed Parker, 31, merited the decision but the Derbyshire fighter experienced the second setback of his 28-fight professional journey.
The Champion Secures Triumph in Slow Match
His career development has slowed in recent years through management issues and considerable time of inactivity.
Previously predicted as the rising talent of British boxing, he now finds himself trying to realize his potential - maybe in what feels like a last chance - under fresh management.
He opened tentatively, with neither fighter prepared to overcommit in a calculated opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury during the bout, was making just his second bout at light heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for Buatsi, who utilized a solid defense to narrowly win the more effective stanzas.
The audience's tolerance decreased during constant clinching, with the challenger slipping to the canvas multiple occasions during grappling.
Parker closed well, but many rounds were hard to judge. However, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, awarding Buatsi just one round.
The victor moves on, but with the presence of hard hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Memorial Inspires Manchester Derby Fight
In the co-main event, Arthur defeated Rea by divided decision in a terrific all-Manchester fight to win the European light-heavyweight title.
The venue grew hushed for a extremely emotional memorial prior to the bout as 10 bells tolled in remembrance of the city's native Hatton, who passed away 46 years old in last month.
It was the first major televised fight night in the urban center since Hatton's passing. As the last bell ended, the quiet transitioned to a chant of "there's just one Ricky Hatton".
The fighting inside the ropes equaled the feeling. Arthur was floored by a powerful punch squarely on the chin in the initial stage, rising shakily to his footing on the referee's count.
But the red-colored attire of Arthur soon came forward again. From the other corner, the opponent - in opposing blue - was marked up quickly, significant bruising appearing under his eye as the fighters exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with stinging uppercuts as the pace hardly diminished over the full distance.
The victor edged the verdict with official scores of draw, narrow lead and 115-112, but the two athletes were determined and courageous, exactly what their inspiration Hatton embodied.
