British light-heavyweight Buatsi secured a victory yet unimpressive debut to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a tight 10-round bout at the Co-op Live Arena.
But Parker found success, connecting with powerful single shots in a contest where the styles didn't complement each other, with frequent clinching marring the contest.
The officials judged it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my greatest performance but how do champions respond? They win," Buatsi stated in the ring as he was faced disapproval from the crowd.
The Londoner bounced back after his initial pro loss - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Various analysts felt the challenger, thirty-one, merited the decision but the Derbyshire fighter suffered the second loss of his 28-match career.
Buatsi Claims Triumph in Uneventful Match
Buatsi's progress has slowed in recent years through promotional disputes and extended periods of lack of fights.
Once tipped as the rising talent of the British fight scene, he now finds himself trying to realize his potential - possibly in what appears to be a last chance - under new promotional backing.
He started carefully, with the two boxers prepared to take risks in a calculated initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand during the bout, was participating in his second appearance at light heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for Buatsi, who operated with a protective stance to edge the more effective stanzas.
The spectators' acceptance diminished because of frequent holding, with Parker going down several times during clinches.
The underdog closed well, but many rounds were difficult to score. However, previous titleholder Carl Frampton - providing analysis for Dazn - had it strongly leaning for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the caliber of power puncher David Benavidez, and Russian champion Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Hatton Memorial Inspires All-Manchester Fight
In the secondary fight, Lyndon Arthur beat Rea by divided decision in a terrific local rivalry contest to win the continental title.
The venue became quiet for a extremely emotional homage ahead of the contest as 10 bells sounded in honor of the city's native Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised fight night in the location since the passing of Hatton. As the final chime faded, the stillness became a shout of "there's just one Ricky Hatton".
The competition within the ring matched the sentiment. Arthur was sent to the canvas by a left hook directly to the face in the initial stage, getting up unsteadily to his position on the count of eight.
But the red-colored equipment of Arthur soon came forward again. Across the ring, the opponent - in competitive blue - was injured soon, noticeable damage developing under his eye as the duo exchanged punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action hardly diminished over 12 rounds.
Arthur edged the decision with official scores of 114-114, 115-113 and wider gap, but each competitor were relentless and brave, exactly what their inspiration the legend stood for.
