British light-heavyweight Buatsi secured a victory yet disappointing debut to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a majority decision in a tight ten-round contest at the boxing arena.
But the challenger found success, landing some telling single shots in a match where the styles failed to mesh, with frequent clinching spoiling the contest.
The officials had it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my greatest showing but how do champions respond? They prevail," Buatsi said in the ring as he was greeted with negative reactions from the spectators.
The Londoner got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers felt the challenger, 31, deserved the win but the Derbyshire fighter experienced the second setback of his 28-fight professional journey.
Buatsi Earns Triumph in Slow Encounter
The fighter's advancement has stalled in the past few years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now finds himself trying to realize his potential - perhaps in what appears to be a last chance - under recent support.
He opened tentatively, with the two boxers willing to take risks in a calculated opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after breaking his hand in the contest, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who worked behind a protective stance to barely take the more effective periods.
The audience's tolerance wore thin amid constant clinching, with the challenger going down several times during clinches.
The underdog closed well, but several stanzas were challenging to assess. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor advances, but with the presence of power puncher David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still appears challenging.
Hatton Homage Fuels Local Rivalry Contest
In the supporting bout, Arthur defeated Rea by close verdict in a terrific local rivalry fight to secure the European light-heavyweight championship.
The venue grew hushed for a profoundly moving memorial ahead of the contest as a bell ceremony rang in honor of local hero Ricky Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the final chime ended, the quiet transitioned to a roar of "there's only one Hatton".
The fighting within the ring equaled the sentiment. The eventual winner was knocked down by a powerful punch squarely on the face in the initial stage, getting up unsteadily to his position on the eight count.
But the traditional red equipment of the fighter soon pressed ahead again. Across the ring, Rea - in rival City blue - was injured early, significant bruising developing under his face as the fighters exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace hardly diminished over the full distance.
The victor narrowly won the verdict with scoring tallies of even score, narrow lead and wider gap, but the two athletes were determined and courageous, everything their hero Hatton stood for.
