British light-heavyweight Buatsi earned a win yet unimpressive start to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a split decision in a close ten-round bout at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful clean blows in a contest where the approaches didn't complement each other, with constant grabbing disrupting the fight.
The officials scored it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my best showing but what do champions do? They prevail," Buatsi commented in the ring as he was greeted with negative reactions from the crowd.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in last winter - to earn a 20th career victory.
Several boxing experts believed Parker, 31, should have been awarded the decision but the contender suffered the second defeat of his 28-match professional journey.
Buatsi Earns Victory in Dull Affair
The fighter's advancement has slowed in recent years through promotional disputes and considerable time of inactivity.
Earlier forecast as the rising talent of UK boxing, he now finds himself trying to realize his potential - possibly in what seems like a last chance - under new promotional backing.
He started carefully, with neither fighter prepared to take risks in a tentative early stages.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was making just his second fight at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, causing problems for the favorite, who worked behind a protective stance to narrowly win the cleaner rounds.
The audience's tolerance diminished because of frequent holding, with the challenger slipping to the canvas various instances during clinches.
The underdog ended stronger, but several stanzas were difficult to score. Nevertheless, previous titleholder Carl Frampton - providing analysis for the broadcast network - 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 Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Memorial Motivates Local Rivalry Fight
In the secondary fight, Arthur overcame Bradley Rea by split-decision in a outstanding all-Manchester fight to win the European light heavyweight belt.
The stadium grew hushed for a profoundly moving tribute before the fight as a bell ceremony rang in remembrance of Manchester's own Ricky Hatton, who succumbed at age 46 in September.
It was the first major televised boxing event in the location since the passing of Hatton. As the final chime faded, the silence became a roar of "there's only one Hatton".
The competition within the ring matched the sentiment. Arthur was sent to the canvas by a powerful punch directly to the jaw in the initial stage, standing uncertainly to his position on the eight count.
But the red-colored shorts of the fighter soon advanced again. On the opposite side, Rea - in rival City blue - was marked up quickly, heavy swelling appearing under his orbital area as the duo traded punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the intensity hardly diminished over twelve rounds.
Arthur narrowly won the result with judges scorecards of 114-114, close margin and clearer margin, but both fighters were relentless and brave, exactly what their idol the legend stood for.
