UK light heavyweight Buatsi earned a win yet underwhelming start to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a split decision in a tight ten-round fight at the Manchester venue.
But the challenger had his moments, landing some telling individual punches in a fight where the approaches didn't complement each other, with frequent clinching marring the contest.
Two judges scored it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my greatest display but what do champions do? They win," the victor said in the ring as he was faced disapproval from the spectators.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to secure a twentieth professional win.
Some ringside observers thought Parker, thirty-one, should have been awarded the win but the Derbyshire fighter experienced the second setback of his 28-bout professional journey.
Buatsi Earns Triumph in Uneventful Match
The fighter's advancement has slowed in recent years through promotional disputes and extended periods of inactivity.
Once tipped as the rising talent of the British fight scene, he now stands trying to fulfil that early promise - possibly in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors prepared to be aggressive in a tentative initial rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after suffering a hand injury in the contest, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for Buatsi, who worked behind a tight guard to narrowly win the more effective rounds.
The crowd's patience diminished during regular grabbing, with Parker going down several times during grappling.
Parker finished the stronger, but multiple periods were challenging to assess. However, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
Buatsi moves on, but with the presence of hard hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - judging by this showing - still appears challenging.
Hatton Homage Motivates All-Manchester Fight
In the co-main event, Lyndon Arthur beat Rea by split-decision in a excellent Manchester vs Manchester contest to win the European light-heavyweight title.
The stadium became quiet for a deeply poignant tribute prior to the bout as 10 bells rang in memory of Manchester's own Hatton, who passed away at age 46 in September.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the final chime ended, the silence gave way to a roar of "only one Hatton".
The action within the ring equaled the sentiment. The eventual winner was floored by a powerful punch directly to the jaw in the initial stage, rising shakily to his footing on the referee's count.
But the traditional red attire of Arthur soon advanced again. Across the ring, the opponent - in opposing blue - was marked up soon, significant bruising appearing under his face as the fighters exchanged hard punches.
The challenger, 27, landed power punches but the champion, 34, fought fire with fire with stinging uppercuts as the intensity rarely dropped over the full distance.
The victor barely secured the result with official scores of 114-114, narrow lead and 115-112, but the two athletes were persistent and brave, exactly what their hero Hatton stood for.
