UK light-heavyweight Buatsi secured a victory yet unimpressive debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a tight 10-round contest at the boxing arena.
But the challenger had his moments, connecting with powerful individual punches in a contest where the approaches didn't complement each other, with constant grabbing disrupting the fight.
The officials scored it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my best showing but what defines champions? They win," Buatsi commented in the arena as he was met by disapproval from the spectators.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers felt Parker, 31, deserved the win but the Derbyshire fighter experienced the second loss of his 28-fight professional journey.
The Champion Earns Triumph in Slow Match
His career development has slowed in recent years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the next star of UK boxing, he now is positioned trying to realize his potential - maybe in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with the two boxers willing to overcommit in a tentative initial rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in 2022 after damaging his hand during the bout, was making just his second bout at light heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for Buatsi, who utilized a solid defense to narrowly win the better rounds.
The audience's tolerance decreased during frequent holding, with the challenger going down various instances during grappling.
Parker closed well, but several stanzas were challenging to assess. Nevertheless, ex-champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
The victor moves on, but with the presence of hard hitter Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Memorial Fuels All-Manchester Fight
In the supporting bout, Lyndon Arthur defeated Bradley Rea by close verdict in a excellent all-Manchester fight to secure the European light-heavyweight championship.
The stadium became quiet for a extremely emotional memorial before the fight as 10 bells tolled in remembrance of the city's native Hatton, who died aged 46 in last month.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the concluding sound disappeared, the quiet gave way to a roar of "there's just one Hatton".
The competition within the ring matched the emotion. The eventual winner was knocked down by a significant blow directly to the jaw in the early round, getting up unsteadily to his footing on the referee's count.
But the Manchester United-red shorts of Arthur soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was damaged quickly, significant bruising developing under his eye as the duo traded powerful shots.
The challenger, 27, connected with strong blows but the champion, 34, responded in kind with powerful upward punches as the pace rarely dropped over twelve rounds.
The victor barely secured the verdict with scoring tallies of 114-114, 115-113 and wider gap, but each competitor were determined and brave, exactly what their hero the legend embodied.
