British light heavyweight Buatsi earned a win yet underwhelming debut to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a competitive ten-round fight at the Co-op Live Arena.
But Parker had his moments, delivering effective individual punches in a fight where the approaches didn't complement each other, with frequent clinching disrupting the action.
Two judges judged it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They succeed," the victor said in the ring as he was faced disapproval from the crowd.
The British fighter returned to winning ways after his first professional defeat - an epic battle with Callum Smith in February - to earn a twentieth professional win.
Various analysts believed the challenger, 31, should have been awarded the victory but the Derbyshire fighter experienced the second setback of his 28-match professional journey.
The Champion Secures Triumph in Slow Affair
His career development has slowed in recent years through promotional disputes and long spells of inactivity.
Previously predicted as the future of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with both competitors prepared to be aggressive in a tentative early stages.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand mid-fight, 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 operated with a tight guard to barely take the more effective rounds.
The spectators' acceptance decreased because of constant clinching, with Parker going down various instances during grappling.
The underdog closed well, but multiple periods were hard to judge. Nevertheless, former world champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
Buatsi advances, but with the likes of heavy hitter Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Homage Fuels Local Rivalry Battle
In the secondary fight, Lyndon Arthur overcame Bradley Rea by divided decision in a terrific all-Manchester battle to secure the continental title.
The venue grew hushed for a deeply poignant tribute prior to the bout as 10 bells sounded in remembrance of the city's native Hatton, who died at age 46 in last month.
It was the first major televised match card in the urban center since Hatton's passing. As the concluding sound disappeared, the quiet gave way to a chant of "there's just one Ricky Hatton".
The fighting during the bout reflected the emotion. The eventual winner was knocked down by a left hook squarely on the face in the initial stage, getting up unsteadily to his footing on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. Across the ring, the opponent - in opposing blue - was damaged soon, heavy swelling appearing under his orbital area as the duo landed hard punches.
Rea, 27, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the action hardly diminished over twelve rounds.
Arthur edged the decision with official scores of even score, 115-113 and 115-112, but both fighters were determined and brave, everything their hero the legend stood for.
