British light-heavyweight Buatsi made a winning yet disappointing debut to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a competitive 10-round contest at the Manchester venue.
But the challenger found success, landing some telling clean blows in a contest where the techniques failed to mesh, with constant grabbing marring the fight.
Two judges scored it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my best showing but how do champions respond? They prevail," Buatsi commented in the arena as he was greeted with boos from the spectators.
The Londoner got back to winning after his initial pro loss - an epic battle with Callum Smith in last winter - to secure a 20th pro success.
Some ringside observers felt the challenger, 31, merited the win but the Derbyshire fighter experienced the second defeat of his 28-bout professional journey.
Buatsi Secures Win in Dull Affair
His career development has slowed in recent times through promotional disputes and extended periods of inactivity.
Once tipped as the next star of the British fight scene, he now stands trying to realize his potential - maybe in what seems like a last chance - under new promotional backing.
He opened tentatively, with neither fighter ready to take risks in a cagey initial rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was making just his second appearance at the higher weight class.
By the halfway stage, the underdog had stayed in contention, causing problems for Buatsi, who worked behind a protective stance to narrowly win the better rounds.
The spectators' acceptance wore thin amid regular grabbing, with the challenger falling to the floor various instances during close exchanges.
Parker finished the stronger, but multiple periods were hard to judge. Nevertheless, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, awarding Buatsi just a single round.
Buatsi advances, but with the presence of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Hatton Tribute Fuels Manchester Derby Fight
In the supporting bout, Lyndon Arthur overcame Rea by divided decision in a excellent Manchester vs Manchester battle to capture the European light-heavyweight title.
The arena became quiet for a profoundly moving tribute before the fight as ten bells rang in honor of local hero Hatton, who died aged 46 in September.
It was the first major televised match card in the city since Hatton's passing. As the last bell faded, the silence became a chant of "only one Ricky Hatton".
The competition during the bout matched the emotion. The eventual winner was floored by a powerful punch directly to the jaw in the initial stage, rising shakily to his position on the eight count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. From the other corner, the opponent - in competitive blue - was injured soon, heavy swelling appearing under his orbital area as the fighters exchanged powerful shots.
Rea, 27, landed power punches but the champion, 34, responded in kind with stinging uppercuts as the intensity seldom decreased over 12 rounds.
Arthur edged the decision with scoring tallies of even score, narrow lead and clearer margin, but the two athletes were determined and brave, exactly what their idol the legend embodied.
