UK light heavyweight Buatsi made a winning yet unimpressive debut to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a tight ten-round bout at the Co-op Live Arena.
But Parker landed significant shots, delivering effective single shots in a fight where the techniques never quite clicked, with excessive holding spoiling the fight.
Two judges scored it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my finest showing but how do champions respond? They win," the victor said in the arena as he was faced disapproval from the audience.
The British fighter got back to winning after his first professional defeat - an thrilling contest with his previous opponent in February - to claim a 20th career victory.
Various analysts thought the challenger, 31, merited the decision but the Derbyshire fighter endured the second loss of his 28-fight career.
Buatsi Secures Victory in Uneventful Affair
Buatsi's progress has stalled in the past few years through promotional disputes and considerable time of lack of fights.
Previously predicted 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 fresh management.
He started carefully, with neither fighter ready to be aggressive in a calculated initial rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was competing in only his second fight at light heavyweight.
By the middle rounds, Parker had stayed in contention, causing problems for the favorite, who operated with a solid defense to narrowly win the more effective stanzas.
The crowd's patience decreased amid regular grabbing, with the challenger going down several times during clinches.
Parker ended stronger, but many rounds were difficult to score. Nevertheless, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
The victor advances, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Hatton Memorial Inspires Local Rivalry Fight
In the secondary fight, Lyndon Arthur defeated Bradley Rea by split-decision in a excellent local rivalry contest to capture the European light-heavyweight belt.
The venue grew hushed for a deeply poignant memorial ahead of the contest as ten bells rang in memory of the city's native Ricky Hatton, who died at age 46 in last month.
It was the first major televised fight night in the city since Hatton's death. As the concluding sound disappeared, the quiet gave way to a roar of "only one Hatton".
The fighting inside the ropes matched the sentiment. Arthur was floored by a powerful punch squarely on the face in the early round, rising shakily to his feet on the referee's count.
But the red-colored attire of the fighter soon advanced again. Across the ring, the opponent - in rival City blue - was damaged soon, significant bruising developing under his eye as the fighters traded punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, fought fire with fire with powerful upward punches as the intensity rarely dropped over 12 rounds.
The victor edged the decision with judges scorecards of draw, 115-113 and wider gap, but each competitor were determined and full of heart, exactly what their inspiration the legend represented.
