UK light-heavyweight Buatsi earned a win yet unimpressive start to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a competitive ten-round fight at the Manchester venue.
But Parker had his moments, landing some telling clean blows in a fight where the approaches failed to mesh, with constant grabbing marring the action.
The scoring judges scored it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest performance but what do champions do? They win," Buatsi said in the arena as he was faced disapproval from the spectators.
The British fighter got back to winning after his initial pro loss - an epic battle with his previous opponent in last winter - to secure a 20th career victory.
Various analysts believed Parker, 31, merited the decision but the Derbyshire fighter endured the second defeat of his 28-match professional journey.
The Champion Earns Win in Slow Match
Buatsi's progress has stalled in recent times through contract problems and extended periods of inactivity.
Previously predicted as the future of UK boxing, he now is positioned trying to realize his potential - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors ready to take risks in a cagey opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for Buatsi, who operated with a protective stance to edge the better stanzas.
The crowd's patience diminished amid regular grabbing, with the challenger falling to the floor various instances during close exchanges.
The underdog finished the stronger, but several stanzas were difficult to score. However, previous titleholder the boxing analyst - working with Dazn - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the caliber of power puncher David Benavidez, and Russian star Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Memorial Motivates Local Rivalry Battle
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a terrific local rivalry battle to capture the continental championship.
The arena became quiet for a extremely emotional memorial ahead of the contest as ten bells rang in remembrance of the city's native Ricky Hatton, who died aged 46 in last month.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the last bell faded, the silence transitioned to a roar of "there's only one Ricky Hatton".
The competition during the bout matched the emotion. The eventual winner was sent to the canvas by a significant blow directly to the jaw in the second round, standing uncertainly to his feet on the count of eight.
But the Manchester United-red shorts of Arthur soon advanced again. From the other corner, the opponent - in competitive blue - was damaged early, significant bruising developing under his eye as the fighters traded punishing blows.
The challenger, 27, delivered effective strikes but the champion, thirty-four, responded in kind with effective uppercuts as the pace rarely dropped over the full distance.
Arthur edged the result with official scores of even score, narrow lead and wider gap, but both fighters were relentless and full of heart, exactly what their idol Hatton represented.
