UK light heavyweight Buatsi secured a victory yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a tight ten-round bout at the Co-op Live Arena.
But Parker had his moments, landing some telling clean blows in a match where the styles never quite clicked, with constant grabbing marring the fight.
The officials scored it 96-94 to the winner, with the third a even score.
"It wasn't my greatest display but what do champions do? They succeed," the victor stated in the ring as he was greeted with boos from the crowd.
The Londoner bounced back after his first professional defeat - an epic battle with his previous opponent in February - to secure a 20th pro success.
Some ringside observers thought the challenger, thirty-one, deserved the win but the Derbyshire fighter experienced the second setback of his 28-bout professional journey.
Buatsi Claims Triumph in Dull Affair
Buatsi's progress has slowed in the past few years through contract problems and extended periods of lack of fights.
Earlier forecast as the future of the British fight scene, he now stands trying to achieve expectations - maybe in what feels like a last chance - under fresh management.
He started carefully, with neither fighter ready to be aggressive in a calculated opening few rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was competing in only his second bout at light-heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a solid defense to narrowly win the more effective stanzas.
The spectators' acceptance decreased during regular grabbing, with the challenger slipping to the canvas various instances during clinches.
Parker closed well, but multiple periods were hard to judge. Although, previous titleholder Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just a single round.
Buatsi moves on, but with the caliber of power puncher David Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Memorial Inspires Manchester Derby Contest
In the co-main event, Lyndon Arthur overcame Rea by divided decision in a outstanding all-Manchester battle to secure the European light-heavyweight championship.
The arena grew hushed for a extremely emotional memorial ahead of the contest as ten bells rang in honor of the city's native Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the concluding sound faded, the quiet gave way to a roar of "there's only one Hatton".
The competition inside the ropes matched the sentiment. Arthur was knocked down by a left hook squarely on the face in the early round, rising shakily to his position on the eight count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. Across the ring, the opponent - in competitive blue - was damaged quickly, noticeable damage appearing under his orbital area as the fighters exchanged hard punches.
Rea, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with powerful upward punches as the pace rarely dropped over 12 rounds.
The victor barely secured the result with official scores of even score, close margin and wider gap, but both fighters were determined and brave, all the qualities their hero Hatton represented.
