UK light-heavyweight Buatsi made a winning yet disappointing debut to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a close ten-round contest at the Manchester venue.
But the challenger had his moments, connecting with powerful single shots in a match where the techniques failed to mesh, with excessive holding disrupting the fight.
Two judges had it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest performance but what do champions do? They succeed," the victor commented in the ringside as he was met by disapproval from the audience.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Several boxing experts thought Parker, 31, should have been awarded the win but the contender experienced the second setback of his 28-match career.
The Champion Claims Triumph in Uneventful Encounter
His career development has plateaued in recent years through promotional disputes and considerable time of lack of fights.
Previously predicted as the rising talent of British boxing, he now is positioned trying to achieve expectations - maybe in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with neither fighter prepared to be aggressive in a tentative opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in two years ago after suffering a hand injury during the bout, was participating in his second fight at light-heavyweight.
By the halfway stage, Parker had made it competitive, creating difficulties for Buatsi, who operated with a solid defense to narrowly win the more effective periods.
The spectators' acceptance diminished because of constant clinching, with Parker falling to the floor various instances during close exchanges.
Parker finished the stronger, but multiple periods were hard to judge. Nevertheless, ex-champion the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just one round.
The victor progresses, but with the likes of hard hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Tribute Motivates Local Rivalry Fight
In the secondary fight, Arthur overcame Rea by split-decision in a outstanding Manchester vs Manchester contest to capture the European light-heavyweight title.
The arena fell silent for a profoundly moving tribute ahead of the contest as 10 bells tolled in memory of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast boxing event in the city since the passing of Hatton. As the final chime faded, the stillness transitioned to a shout of "there's only one Ricky Hatton".
The action during the bout matched the emotion. The eventual winner was sent to the canvas by a significant blow flush on the face in the second round, standing uncertainly to his feet on the referee's count.
But the traditional red shorts of Arthur soon pressed ahead again. From the other corner, Rea - in competitive blue - was damaged quickly, heavy swelling developing under his eye as the fighters traded powerful shots.
The challenger, 27, delivered effective strikes but Arthur, 34, matched the intensity with stinging uppercuts as the pace rarely dropped over twelve rounds.
The victor edged the result with scoring tallies of draw, 115-113 and 115-112, but both fighters were persistent and full of heart, all the qualities their idol Hatton embodied.
