UK light-heavyweight Buatsi secured a victory yet disappointing beginning to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a majority decision in a tight 10-round bout at the Co-op Live Arena.
But Parker landed significant shots, delivering effective individual punches in a fight where the styles never quite clicked, with excessive holding spoiling the fight.
The scoring judges had it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest performance but what defines champions? They succeed," Buatsi stated in the arena as he was greeted with negative reactions from the spectators.
The British fighter bounced back after his maiden career setback - an epic battle with Callum Smith in February - to earn a twentieth professional win.
Several boxing experts felt Parker, thirty-one, deserved the win but the British boxer experienced the second defeat of his 28-bout professional journey.
Buatsi Claims Triumph in Uneventful Affair
Buatsi's progress has stalled in recent times through contract problems and extended periods of lack of fights.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to realize his potential - perhaps in what appears to be a final roll of the dice - under recent support.
He started carefully, with neither fighter willing to overcommit in a cagey early stages.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after breaking his hand in the contest, was making just his second fight at light-heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for the favorite, who worked behind a tight guard to narrowly win the better periods.
The crowd's patience diminished amid constant clinching, with Parker falling to the floor various instances during clinches.
The underdog ended stronger, but several stanzas were hard to judge. However, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for the challenger, giving Buatsi just only one stanza.
The victor advances, but with the caliber of heavy hitter Benavidez, and Russian star Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Hatton Homage Motivates All-Manchester Battle
In the co-main event, Lyndon Arthur defeated Bradley Rea by divided decision in a terrific local rivalry contest to capture the European light-heavyweight belt.
The arena became quiet for a deeply poignant tribute before the fight as a bell ceremony rang in remembrance of Manchester's own Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast match card in the location since Hatton's passing. As the last bell ended, the silence became a roar of "only one Hatton".
The competition inside the ropes equaled the sentiment. Arthur was knocked down by a left hook flush on the face in the second round, getting up unsteadily to his position on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. From the other corner, Rea - in competitive blue - was marked up quickly, significant bruising forming under his face as the fighters exchanged powerful shots.
The challenger, 27, landed power punches but the champion, 34, fought fire with fire with effective uppercuts as the intensity rarely dropped over 12 rounds.
The victor narrowly won the decision with scoring tallies of even score, narrow lead and wider gap, but each competitor were relentless and full of heart, everything their idol Hatton represented.
