British light-heavyweight Buatsi secured a victory yet unimpressive start to life under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a competitive 10-round contest at the boxing arena.
But Parker had his moments, connecting with powerful individual punches in a match where the styles failed to mesh, with excessive holding disrupting the contest.
Two judges judged it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my greatest showing but how do champions respond? They win," Buatsi stated in the ringside as he was greeted with boos from the crowd.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to claim a 20th pro success.
Various analysts felt the challenger, thirty-one, merited the win but the Derbyshire fighter experienced the second defeat of his 28-bout professional journey.
Buatsi Claims Victory in Dull Affair
His career development has stalled in recent times through contract problems and extended periods of lack of fights.
Earlier forecast as the rising talent of British boxing, he now stands trying to fulfil that early promise - maybe in what seems like a last chance - under new promotional backing.
He began cautiously, with both competitors willing to be aggressive in a tentative opening few rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand mid-fight, was participating in his second appearance at light heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for the favorite, who utilized a protective stance to edge the more effective rounds.
The spectators' acceptance wore thin during constant clinching, with the challenger going down various instances during clinches.
Parker ended stronger, but many rounds were hard to judge. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the likes of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Homage Inspires Local Rivalry Battle
In the co-main event, Arthur defeated Bradley Rea by split-decision in a excellent local rivalry battle to capture the European light-heavyweight championship.
The arena fell silent for a deeply poignant memorial prior to the bout as ten bells rang in remembrance of Manchester's own Ricky Hatton, who succumbed at age 46 in recently.
It was the first major televised boxing event in the city since Hatton's passing. As the last bell disappeared, the silence gave way to a roar of "there's just one Ricky Hatton".
The fighting during the bout equaled the emotion. The eventual winner was floored by a left hook directly to the chin in the second round, rising shakily to his footing on the count of eight.
But the Manchester United-red shorts of the fighter soon pressed ahead again. Across the ring, Rea - in competitive blue - was marked up soon, heavy swelling forming under his orbital area as the duo landed powerful shots.
The challenger, 27, connected with strong blows but Arthur, thirty-four, matched the intensity with stinging uppercuts as the action hardly diminished over twelve rounds.
Arthur barely secured the result with official scores of 114-114, 115-113 and clearer margin, but both fighters were determined and full of heart, everything their hero the legend stood for.
