British light-heavyweight Buatsi made a winning yet unimpressive debut to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a competitive 10-round contest at the Manchester venue.
But Parker had his moments, landing some telling single shots in a contest where the approaches didn't complement each other, with constant grabbing spoiling the fight.
Two judges scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my greatest showing but what defines champions? They succeed," Buatsi commented in the ring as he was greeted with negative reactions from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Some ringside observers believed the challenger, thirty-one, deserved the win but the Derbyshire fighter suffered the second defeat of his 28-bout professional journey.
Buatsi Secures Victory in Slow Affair
The fighter's advancement has stalled in the past few years through promotional disputes and long spells of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to achieve expectations - perhaps in what feels like a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors willing to overcommit in a calculated initial rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was participating in his second bout at light-heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for the favorite, who worked behind a solid defense to edge the better rounds.
The crowd's patience wore thin during frequent holding, with Parker slipping to the canvas multiple occasions during grappling.
Parker ended stronger, but many rounds were challenging to assess. Although, former world champion Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just only one stanza.
The victor progresses, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Homage Fuels All-Manchester Battle
In the secondary fight, Lyndon Arthur beat Bradley Rea by close verdict in a excellent all-Manchester contest to capture the continental championship.
The arena became quiet for a deeply poignant memorial before the fight as ten bells rang in remembrance of Manchester's own Hatton, who died aged 46 in September.
It was the first major televised fight night in the urban center since Hatton's death. As the last bell disappeared, the silence gave way to a roar of "there's only one Hatton".
The competition within the ring reflected the feeling. The eventual winner was floored by a significant blow squarely on the jaw in the early round, rising shakily to his footing on the eight count.
But the red-colored equipment of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was injured soon, significant bruising forming under his orbital area as the fighters exchanged powerful shots.
The challenger, twenty-seven, connected with strong blows but the champion, 34, fought fire with fire with powerful upward punches as the pace seldom decreased over the full distance.
Arthur narrowly won the result with scoring tallies of 114-114, 115-113 and clearer margin, but both fighters were relentless and courageous, everything their inspiration the legend embodied.
