British light-heavyweight Buatsi secured a victory yet disappointing beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a majority decision in a tight 10-round fight at the boxing arena.
But Parker had his moments, delivering effective clean blows in a fight where the techniques failed to mesh, with constant grabbing spoiling the fight.
Two judges had it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my finest display but what defines champions? They succeed," Buatsi commented in the arena as he was met by disapproval from the spectators.
The British fighter bounced back after his initial pro loss - an epic battle with Callum Smith in last winter - to secure a 20th career victory.
Several boxing experts thought Parker, thirty-one, merited the decision but the contender suffered the second defeat of his 28-match career.
Buatsi Secures Triumph in Dull Affair
The fighter's advancement has stalled in recent years through contract problems and long spells of inactivity.
Once tipped as the future of the British fight scene, he now stands trying to achieve expectations - maybe in what feels like a last chance - under recent support.
He began cautiously, with both competitors ready to overcommit in a cagey opening few rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after suffering a hand injury during the bout, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for the favorite, who worked behind a protective stance to edge the cleaner rounds.
The spectators' acceptance wore thin because of frequent holding, with Parker going down several times during clinches.
Parker finished the stronger, but several stanzas were difficult to score. Although, ex-champion Carl Frampton - commentating on Dazn - had it significantly in favor for Parker, scoring for Buatsi just one round.
The victor progresses, but with the presence of hard hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Tribute Fuels Local Rivalry Contest
In the co-main event, Lyndon Arthur defeated Rea by split-decision in a terrific local rivalry battle to capture the continental title.
The venue fell silent for a deeply poignant memorial prior to the bout as ten bells sounded in memory of local hero Hatton, who succumbed 46 years old in last month.
It was the premier televised fight night in the location since the passing of Hatton. As the last bell ended, the silence gave way to a roar of "only one Ricky Hatton".
The action inside the ropes matched the feeling. Arthur was knocked down by a significant blow directly to the jaw in the second round, standing uncertainly to his footing on the referee's count.
But the Manchester United-red shorts of Arthur soon pressed ahead again. Across the ring, Rea - in rival City blue - was damaged soon, significant bruising developing under his orbital area as the fighters exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with stinging uppercuts as the intensity hardly diminished over the full distance.
Arthur barely secured the decision with official scores of draw, 115-113 and wider gap, but the two athletes were determined and brave, exactly what their idol Hatton embodied.
