British light heavyweight Buatsi made a winning yet disappointing start to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a close ten-round contest at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful clean blows in a contest where the techniques didn't complement each other, with constant grabbing spoiling the action.
Two judges judged it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my finest display but how do champions respond? They succeed," Buatsi stated in the ringside as he was met by disapproval from the crowd.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to secure a 20th career victory.
Several boxing experts thought the challenger, 31, deserved the decision but the contender experienced the second loss of his 28-bout career.
The Champion Claims Win in Uneventful Encounter
The fighter's advancement has plateaued in recent years through promotional disputes and extended periods of inactivity.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to achieve expectations - maybe in what appears to be a last chance - under new promotional backing.
He started carefully, with neither fighter ready to take risks in a tentative opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand in the contest, was making just his second fight at the higher weight class.
By the halfway stage, Parker had kept it close, creating difficulties for the favorite, who utilized a protective stance to narrowly win the better rounds.
The crowd's patience wore thin because of constant clinching, with the challenger falling to the floor various instances during grappling.
Parker finished the stronger, but several stanzas were challenging to assess. Nevertheless, former world champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
Buatsi advances, but with the caliber of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Tribute Inspires Local Rivalry Contest
In the co-main event, Arthur overcame Rea by close verdict in a excellent local rivalry contest to secure the European light heavyweight title.
The venue fell silent for a extremely emotional memorial before the fight as 10 bells rang in remembrance of the city's native Hatton, who succumbed aged 46 in last month.
It was the first major televised fight night in the city since the passing of Hatton. As the final chime disappeared, the silence gave way to a roar of "there's only one Hatton".
The competition inside the ropes reflected the sentiment. The eventual winner was sent to the canvas by a left hook flush on the jaw in the second round, standing uncertainly to his position on the count of eight.
But the red-colored shorts of Arthur soon pressed ahead again. Across the ring, the opponent - in opposing blue - was marked up soon, noticeable damage developing under his eye as the pair exchanged punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with effective uppercuts as the action seldom decreased over twelve rounds.
Arthur edged the verdict with judges scorecards of even score, close margin and wider gap, but both fighters were relentless and full of heart, exactly what their inspiration the legend stood for.
