British light-heavyweight Buatsi secured a victory yet unimpressive start to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a majority decision in a tight ten-round fight at the Manchester venue.
But Parker had his moments, landing some telling individual punches in a contest where the approaches failed to mesh, with frequent clinching spoiling the action.
The scoring judges had it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my finest performance but how do champions respond? They win," Buatsi stated in the ring as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in last winter - to secure a 20th career victory.
Some ringside observers thought Parker, 31, merited the decision but the British boxer suffered the second loss of his 28-bout career.
Buatsi Secures Win in Dull Encounter
His career development has stalled in recent years through contract problems and long spells of inactivity.
Once tipped as the future of the British fight scene, he now is positioned trying to realize his potential - maybe in what seems like a last chance - under new promotional backing.
He began cautiously, with the two boxers willing to take risks in a calculated early stages.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after breaking his hand during the bout, was making just his second fight at light-heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for the favorite, who worked behind a tight guard to barely take the better periods.
The audience's tolerance wore thin because of frequent holding, with the challenger going down various instances during close exchanges.
Parker finished the stronger, but several stanzas were challenging to assess. However, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
The victor advances, but with the caliber of power puncher David Benavidez, and Russian star Bivol leading the category, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Tribute Motivates Local Rivalry Fight
In the secondary fight, Lyndon Arthur overcame Rea by divided decision in a outstanding local rivalry battle to secure the European light heavyweight belt.
The stadium grew hushed for a deeply poignant tribute ahead of the contest as a bell ceremony sounded in memory of Manchester's own Ricky Hatton, who succumbed aged 46 in recently.
It was the first major televised fight night in the location since the passing of Hatton. As the concluding sound faded, the silence gave way to a chant of "only one Hatton".
The fighting within the ring reflected the feeling. Arthur was sent to the canvas by a significant blow squarely on the face in the initial stage, standing uncertainly to his footing on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. Across the ring, Rea - in competitive blue - was damaged quickly, noticeable damage developing under his orbital area as the duo landed hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with powerful upward punches as the pace hardly diminished over the full distance.
The victor narrowly won the verdict with official scores of even score, 115-113 and clearer margin, but the two athletes were relentless and brave, all the qualities their idol the legend stood for.
