British light-heavyweight Buatsi secured a victory yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a tight 10-round bout at the boxing arena.
But the challenger had his moments, delivering effective clean blows in a match where the approaches never quite clicked, with excessive holding disrupting the fight.
The officials had it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my best showing but what defines champions? They prevail," Buatsi said in the ring as he was faced negative reactions from the crowd.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in last winter - to claim a twentieth professional win.
Several boxing experts felt the challenger, 31, deserved the decision but the British boxer endured the second defeat of his 28-fight professional journey.
Buatsi Earns Win in Uneventful Match
His career development has plateaued in the past few years through contract problems and considerable time of inactivity.
Previously predicted as the future of UK boxing, he now stands trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with neither fighter prepared to be aggressive in a calculated opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand during the bout, was competing in only his second bout at the higher weight class.
By the fight's midpoint, Parker had kept it close, causing problems for the favorite, who utilized a tight guard to barely take the better stanzas.
The crowd's patience decreased amid regular grabbing, with the challenger falling to the floor various instances during close exchanges.
Parker ended stronger, but many rounds were hard to judge. However, ex-champion the boxing analyst - commentating on Dazn - had it strongly leaning for Parker, giving Buatsi just only one stanza.
Buatsi moves on, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Hatton Tribute Fuels Manchester Derby Fight
In the co-main event, Lyndon Arthur beat Rea by split-decision in a outstanding local rivalry contest to secure the European light-heavyweight title.
The stadium became quiet for a extremely emotional homage prior to the bout as 10 bells tolled in remembrance of local hero Hatton, who died at age 46 in last month.
It was the first major televised fight night in the location since Hatton's passing. As the last bell ended, the stillness gave way to a shout of "there's just one Hatton".
The action inside the ropes matched the sentiment. Arthur was knocked down by a left hook directly to the chin in the second round, rising shakily to his feet on the count of eight.
But the Manchester United-red attire of Arthur soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was damaged early, significant bruising appearing under his eye as the pair exchanged hard punches.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the pace hardly diminished over the full distance.
Arthur edged the result with judges scorecards of draw, 115-113 and clearer margin, but both fighters were determined and full of heart, everything their hero the legend represented.
