British light-heavyweight Buatsi earned a win yet underwhelming debut to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a tight ten-round contest at the Manchester venue.
But the challenger had his moments, landing some telling individual punches in a contest where the styles never quite clicked, with excessive holding spoiling the action.
The officials scored it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my greatest display but what do champions do? They win," Buatsi stated in the ringside as he was greeted with disapproval from the crowd.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in February - to claim a 20th pro success.
Some ringside observers believed Parker, thirty-one, should have been awarded the win but the contender experienced the second defeat of his 28-bout career.
Buatsi Earns Triumph in Dull Match
His career development has slowed in recent times through management issues and considerable time of lack of fights.
Once tipped as the future of British boxing, he now finds himself trying to fulfil that early promise - possibly in what appears to be a last chance - under new promotional backing.
He opened tentatively, with the two boxers ready to overcommit in a cagey opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after damaging his hand mid-fight, was competing in only his second fight at light heavyweight.
By the middle rounds, Parker had kept it close, causing problems for Buatsi, who operated with a solid defense to narrowly win the cleaner rounds.
The spectators' acceptance decreased because of constant clinching, with the challenger falling to the floor various instances during clinches.
The underdog closed well, but several stanzas were difficult to score. However, former world champion Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, giving Buatsi just a single round.
The victor advances, but with the presence of power puncher Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Memorial Fuels All-Manchester Contest
In the co-main event, Arthur overcame Bradley Rea by divided decision in a excellent Manchester vs Manchester fight to win the continental championship.
The arena fell silent for a profoundly moving memorial before the fight as 10 bells rang in honor of local hero Ricky Hatton, who succumbed aged 46 in recently.
It was the first major televised match card in the location since Hatton's passing. As the final chime disappeared, the stillness became a chant of "there's just one Hatton".
The fighting inside the ropes matched the feeling. The eventual winner was sent to the canvas by a left hook directly to the face in the initial stage, standing uncertainly to his footing on the referee's count.
But the red-colored shorts of Arthur soon came forward again. On the opposite side, Rea - in rival City blue - was marked up soon, noticeable damage developing under his face as the pair exchanged hard punches.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace rarely dropped over the full distance.
The victor edged the verdict with judges scorecards of even score, narrow lead and clearer margin, but each competitor were persistent and courageous, exactly what their inspiration the legend embodied.
