UK light heavyweight Buatsi made a winning yet unimpressive beginning to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a close 10-round contest at the Co-op Live Arena.
But Parker found success, landing some telling clean blows in a contest where the styles never quite clicked, with frequent clinching spoiling the action.
The officials scored it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my best performance but what do champions do? They win," Buatsi said in the ringside as he was met by disapproval from the spectators.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a 20th career victory.
Various analysts thought the challenger, thirty-one, should have been awarded the decision but the British boxer experienced the second defeat of his 28-fight career.
The Champion Earns Triumph in Slow Encounter
His career development has plateaued in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now stands trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under recent support.
He opened tentatively, with the two boxers willing to overcommit in a tentative early stages.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in two years ago after breaking his hand in the contest, was making just his second fight at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who utilized a protective stance to edge the cleaner rounds.
The crowd's patience decreased amid frequent holding, with the challenger going down multiple occasions during close exchanges.
Parker finished the stronger, but several stanzas were hard to judge. However, ex-champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
Buatsi advances, but with the caliber of hard hitter David Benavidez, and Russian star Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Hatton Homage Inspires Local Rivalry Fight
In the supporting bout, Lyndon Arthur beat Bradley Rea by split-decision in a outstanding all-Manchester fight to capture the European light-heavyweight title.
The arena fell silent for a extremely emotional memorial ahead of the contest as a bell ceremony sounded in honor of local hero Hatton, who passed away at age 46 in recently.
It was the premier televised fight night in the location since Hatton's death. As the concluding sound disappeared, the silence gave way to a shout of "there's just one Ricky Hatton".
The competition inside the ropes matched the feeling. Arthur was floored by a significant blow flush on the face in the early round, getting up unsteadily to his footing on the referee's count.
But the traditional red equipment of the fighter soon advanced again. From the other corner, Rea - in rival City blue - was injured soon, heavy swelling developing under his orbital area as the duo landed punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with powerful upward punches as the intensity seldom decreased over the full distance.
The victor narrowly won the decision with judges scorecards of even score, narrow lead and wider gap, but each competitor were determined and courageous, everything their inspiration the legend embodied.
