UK light-heavyweight Buatsi earned a win yet unimpressive debut to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a tight ten-round fight at the boxing arena.
But the challenger had his moments, landing some telling clean blows in a contest where the approaches never quite clicked, with frequent clinching disrupting the fight.
The officials had it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my finest display but how do champions respond? They prevail," the victor commented in the ringside as he was greeted with boos from the crowd.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Several boxing experts felt Parker, thirty-one, merited the victory but the Derbyshire fighter suffered the second setback of his 28-fight professional journey.
The Champion Earns Triumph in Slow Match
His career development has slowed in the past few years through promotional disputes and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now stands trying to achieve expectations - possibly in what appears to be a last chance - under recent support.
He started carefully, with both competitors ready to overcommit 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 breaking his hand during the bout, was making just his second appearance at light heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for the favorite, who operated with a protective stance to barely take the more effective rounds.
The crowd's patience wore thin amid regular grabbing, with the challenger falling to the floor various instances during clinches.
Parker closed well, but multiple periods were difficult to score. Nevertheless, previous titleholder the boxing analyst - working with the broadcast network - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
Buatsi advances, but with the likes of power puncher David Benavidez, and Russian champion Bivol leading the category, the journey to titles - judging by this showing - still looks steep.
Hatton Tribute Fuels Local Rivalry Fight
In the secondary fight, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific Manchester vs Manchester battle to capture the continental belt.
The stadium became quiet for a extremely emotional memorial before the fight as a bell ceremony tolled in honor of the city's native Ricky Hatton, who succumbed 46 years old in recently.
It was the first major televised fight night in the urban center since the passing of Hatton. As the final chime faded, the silence became a chant of "there's just one Hatton".
The action inside the ropes reflected the sentiment. The eventual winner was sent to the canvas by a left hook directly to the face in the early round, getting up unsteadily to his position on the referee's count.
But the traditional red equipment of the fighter soon pressed ahead again. Across the ring, the opponent - in rival City blue - was injured soon, significant bruising developing under his orbital area as the pair exchanged punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with effective uppercuts as the pace hardly diminished over 12 rounds.
The victor narrowly won the decision with judges scorecards of draw, narrow lead and clearer margin, but the two athletes were persistent and full of heart, exactly what their inspiration Hatton stood for.
