UK light heavyweight Buatsi made a winning yet unimpressive debut to life under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a close ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful clean blows in a contest where the styles didn't complement each other, with frequent clinching marring the contest.
The officials scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my best display but what do champions do? They win," the victor said in the ringside as he was faced boos from the spectators.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Various analysts felt Parker, thirty-one, should have been awarded the win but the Derbyshire fighter endured the second loss of his 28-bout professional journey.
The Champion Earns Win in Uneventful Match
The fighter's advancement has slowed in recent years through promotional disputes and extended periods of lack of fights.
Once tipped as the future of British boxing, he now is positioned trying to achieve expectations - perhaps in what feels like a ultimate opportunity - under recent support.
He began cautiously, with the two boxers ready to overcommit in a cagey opening few rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after breaking his hand in the contest, was competing in only his second bout at light-heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who worked behind a protective stance to barely take the cleaner rounds.
The spectators' acceptance decreased because of frequent holding, with Parker going down various instances during clinches.
Parker ended stronger, but multiple periods were difficult to score. However, former world champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, giving Buatsi just one round.
The victor progresses, but with the likes of hard hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Memorial Inspires All-Manchester Fight
In the secondary fight, Lyndon Arthur beat Bradley Rea by split-decision in a outstanding local rivalry contest to win the European light heavyweight belt.
The venue became quiet for a deeply poignant tribute before the fight as 10 bells sounded in remembrance of local hero Hatton, who succumbed aged 46 in September.
It was the first major televised fight night in the urban center since the passing of Hatton. As the last bell faded, the stillness became a chant of "there's only one Ricky Hatton".
The competition during the bout matched the emotion. Arthur was knocked down by a powerful punch flush on the jaw in the initial stage, standing uncertainly to his footing on the count of eight.
But the traditional red attire of the fighter soon advanced again. Across the ring, the opponent - in opposing blue - was marked up soon, significant bruising forming under his face as the pair exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with powerful upward punches as the intensity rarely dropped over the full distance.
The victor narrowly won the decision with official scores of draw, close margin and clearer margin, but both fighters were determined and courageous, everything their hero the legend stood for.
