UK light-heavyweight Buatsi earned a win yet unimpressive beginning to his career under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a competitive ten-round fight at the Co-op Live Arena.
But Parker landed significant shots, landing some telling individual punches in a match where the approaches didn't complement each other, with frequent clinching marring the fight.
The officials had it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They succeed," the victor said in the ringside as he was faced negative reactions from the audience.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in last winter - to earn a 20th pro success.
Some ringside observers believed the challenger, 31, deserved the victory but the Derbyshire fighter endured the second setback of his 28-fight career.
Buatsi Claims Win in Dull Affair
His career development has stalled in recent times through management issues and extended periods of lack of fights.
Once tipped as the rising talent of UK boxing, he now stands trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He began cautiously, with both competitors ready to take risks in a calculated opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was participating in his second appearance at the higher weight class.
By the halfway stage, the underdog had kept it close, creating difficulties for the favorite, who operated with a tight guard to barely take the more effective rounds.
The spectators' acceptance wore thin amid constant clinching, with Parker slipping to the canvas various instances during grappling.
Parker finished the stronger, but several stanzas were difficult to score. Nevertheless, ex-champion Carl Frampton - working with Dazn - had it significantly in favor for Parker, giving Buatsi just one round.
The victor moves on, but with the likes of hard hitter Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Tribute Fuels Manchester Derby Battle
In the secondary fight, Arthur beat Bradley Rea by close verdict in a terrific Manchester vs Manchester battle to win the European light heavyweight belt.
The stadium grew hushed for a extremely emotional memorial prior to the bout as ten bells rang in memory of local hero Ricky Hatton, who died aged 46 in recently.
It was the first major televised boxing event in the city since the passing of Hatton. As the final chime ended, the quiet gave way to a roar of "only one Ricky Hatton".
The fighting during the bout reflected the feeling. The eventual winner was floored by a powerful punch directly to the face in the early round, getting up unsteadily to his footing on the count of eight.
But the Manchester United-red equipment of the fighter soon came forward again. On the opposite side, Rea - in rival City blue - was damaged early, heavy swelling developing under his eye as the fighters landed hard punches.
The challenger, 27, landed power punches but the champion, 34, fought fire with fire with powerful upward punches as the intensity rarely dropped over twelve rounds.
The victor edged the verdict with judges scorecards of draw, 115-113 and wider gap, but the two athletes were persistent and full of heart, everything their inspiration Hatton stood for.
