British light heavyweight Buatsi earned a win yet unimpressive debut to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a majority decision in a competitive ten-round contest at the boxing arena.
But Parker found success, connecting with powerful clean blows in a fight where the styles didn't complement each other, with frequent clinching marring the contest.
The officials had it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my best display but what defines champions? They prevail," the victor stated in the arena as he was faced negative reactions from the crowd.
The British fighter bounced back after his first professional defeat - an epic battle with his previous opponent in February - to earn a twentieth professional win.
Some ringside observers thought Parker, thirty-one, deserved the decision but the contender suffered the second setback of his 28-bout professional journey.
Buatsi Secures Victory in Dull Affair
His career development has slowed in recent times through promotional disputes and extended periods of inactivity.
Once tipped as the rising talent of British boxing, he now stands trying to realize his potential - maybe in what seems like a ultimate opportunity - under fresh management.
He started carefully, with neither fighter prepared to be aggressive in a calculated opening few rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was competing in only his second fight at the higher weight class.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who operated with a protective stance to edge the better periods.
The audience's tolerance diminished because of regular grabbing, with Parker slipping to the canvas various instances during close exchanges.
The underdog finished the stronger, but multiple periods were challenging to assess. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just one round.
Buatsi progresses, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Hatton Homage Inspires All-Manchester Contest
In the supporting bout, Lyndon Arthur beat Rea by close verdict in a excellent Manchester vs Manchester battle to secure the European light-heavyweight belt.
The venue became quiet for a profoundly moving tribute ahead of the contest as ten bells rang in memory of local hero Ricky Hatton, who passed away at age 46 in September.
It was the initial significant broadcast match card in the location since Hatton's passing. As the concluding sound ended, the quiet transitioned to a chant of "there's just one Hatton".
The competition inside the ropes equaled the sentiment. Arthur was sent to the canvas by a significant blow squarely on the face in the early round, standing uncertainly to his position on the count of eight.
But the Manchester United-red attire of the fighter soon advanced again. From the other corner, the opponent - in opposing blue - was injured soon, significant bruising developing under his face as the fighters exchanged hard punches.
Rea, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace seldom decreased over the full distance.
Arthur barely secured the result with official scores of draw, narrow lead and 115-112, but each competitor were relentless and courageous, everything their inspiration the legend stood for.
