UK light heavyweight Buatsi made a winning yet underwhelming debut to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a majority decision in a competitive 10-round fight at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful single shots in a fight where the techniques never quite clicked, with constant grabbing marring the action.
The officials had it 96-94 to the winner, with the third a 95-95.
"It wasn't my greatest display but what do champions do? They prevail," Buatsi stated in the ring as he was faced disapproval from the crowd.
The Londoner returned to winning ways after his initial pro loss - an epic battle with his previous opponent in February - to earn a twentieth professional win.
Various analysts felt the challenger, thirty-one, deserved the victory but the contender experienced the second loss of his 28-fight career.
The Champion Secures Victory in Slow Encounter
His career development has plateaued in recent years through contract problems and extended periods of inactivity.
Once tipped as the rising talent of the British fight scene, he now finds himself trying to realize his potential - maybe in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with neither fighter willing to overcommit in a cagey opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was making just his second fight at the higher weight class.
By the middle rounds, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a tight guard to edge the more effective stanzas.
The spectators' acceptance diminished amid frequent holding, with Parker slipping to the canvas several times during clinches.
Parker ended stronger, but multiple periods were difficult to score. Although, former world champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, awarding Buatsi just one round.
The victor advances, but with the presence of hard hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Tribute Motivates Local Rivalry Contest
In the supporting bout, Arthur overcame Rea by divided decision in a outstanding local rivalry battle to capture the continental title.
The arena fell silent for a deeply poignant homage before the fight as ten bells sounded in memory of the city's native Hatton, who passed away aged 46 in September.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the last bell ended, the silence became a shout of "only one Hatton".
The action during the bout equaled the sentiment. The eventual winner was knocked down by a significant blow directly to the chin in the early round, standing uncertainly to his feet on the referee's count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. Across the ring, Rea - in opposing blue - was marked up early, noticeable damage appearing under his orbital area as the duo landed punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, responded in kind with powerful upward punches as the action seldom decreased over 12 rounds.
Arthur barely secured the verdict with official scores of draw, narrow lead and clearer margin, but each competitor were persistent and full of heart, all the qualities their idol the legend embodied.
