UK light-heavyweight Buatsi earned a win yet unimpressive debut to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a split decision in a close 10-round contest at the boxing arena.
But Parker found success, landing some telling individual punches in a fight where the styles didn't complement each other, with constant grabbing marring the action.
The officials had it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest display but what do champions do? They succeed," Buatsi stated in the arena as he was met by boos from the crowd.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in February - to claim a 20th career victory.
Several boxing experts felt the challenger, 31, deserved the decision but the contender experienced the second defeat of his 28-fight professional journey.
Buatsi Earns Victory in Uneventful Encounter
The fighter's advancement has slowed in recent times through contract problems and long spells of lack of fights.
Previously predicted as the rising talent of British boxing, he now stands trying to realize his potential - possibly in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with neither fighter prepared to overcommit in a calculated early stages.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after damaging his hand during the bout, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who worked behind a tight guard to narrowly win the better rounds.
The audience's tolerance decreased during regular grabbing, with Parker slipping to the canvas various instances during clinches.
Parker ended stronger, but multiple periods were difficult to score. Nevertheless, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor moves on, but with the caliber of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Tribute Fuels All-Manchester Battle
In the secondary fight, Lyndon Arthur defeated Bradley Rea by divided decision in a outstanding all-Manchester fight to capture the European light heavyweight championship.
The stadium grew hushed for a deeply poignant memorial before the fight as ten bells rang in memory of Manchester's own Hatton, who succumbed 46 years old in September.
It was the premier televised fight night in the city since the passing of Hatton. As the last bell ended, the stillness gave way to a chant of "there's just one Hatton".
The competition inside the ropes equaled the feeling. The eventual winner was knocked down by a powerful punch flush on the chin in the second round, standing uncertainly to his position on the referee's count.
But the Manchester United-red equipment of the fighter soon advanced again. On the opposite side, Rea - in opposing blue - was injured early, heavy swelling forming under his face as the pair traded hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with powerful upward punches as the intensity hardly diminished over twelve rounds.
Arthur narrowly won the verdict with official scores of even score, 115-113 and wider gap, but the two athletes were determined and courageous, everything their idol Hatton represented.
