UK light-heavyweight Buatsi made a winning yet disappointing beginning to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a majority decision in a competitive ten-round contest at the Co-op Live Arena.
But the challenger found success, connecting with powerful clean blows in a fight where the styles never quite clicked, with frequent clinching spoiling the action.
Two judges had it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my finest performance but what do champions do? They prevail," the victor said in the arena as he was greeted with negative reactions from the audience.
The Londoner bounced back after his initial pro loss - an memorable fight with his previous opponent in February - to claim a 20th pro success.
Various analysts felt Parker, thirty-one, deserved the victory but the British boxer experienced the second setback of his 28-bout professional journey.
The Champion Claims Victory in Dull Encounter
The fighter's advancement has plateaued in the past few years through promotional disputes and considerable time of inactivity.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to realize his potential - maybe in what appears to be a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter willing to be aggressive in a tentative initial rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was participating in his second bout at light-heavyweight.
By the middle rounds, Parker had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to edge the better stanzas.
The crowd's patience diminished during regular grabbing, with Parker going down several times during clinches.
The underdog ended stronger, but many rounds were hard to judge. However, ex-champion the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, awarding Buatsi just a single round.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Homage Fuels Local Rivalry Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding local rivalry battle to secure the European light heavyweight championship.
The venue grew hushed for a deeply poignant tribute before the fight as ten bells rang in honor of local hero Ricky Hatton, who succumbed 46 years old in recently.
It was the first major televised fight night in the city since Hatton's passing. As the concluding sound disappeared, the quiet transitioned to a shout of "only one Ricky Hatton".
The competition within the ring equaled the sentiment. The eventual winner was sent to the canvas by a significant blow flush on the chin in the initial stage, rising shakily to his position on the eight count.
But the Manchester United-red shorts of Arthur soon came forward again. From the other corner, Rea - in rival City blue - was marked up early, heavy swelling developing under his face as the pair exchanged powerful shots.
The challenger, twenty-seven, landed power punches but the champion, 34, responded in kind with effective uppercuts as the action hardly diminished over the full distance.
Arthur narrowly won the verdict with official scores of draw, narrow lead and wider gap, but the two athletes were determined and courageous, all the qualities their idol the legend represented.
