British light-heavyweight Buatsi made a winning yet unimpressive start to his career under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a close ten-round fight at the Co-op Live Arena.
But the challenger had his moments, landing some telling clean blows in a match where the approaches didn't complement each other, with frequent clinching spoiling the action.
The scoring judges judged it 96-94 for to the winner, with the final judge a even score.
"It wasn't my finest showing but how do champions respond? They prevail," Buatsi stated in the ringside as he was faced disapproval from the audience.
The Londoner bounced back after his initial pro loss - an epic battle with Callum Smith in last winter - to secure a 20th pro success.
Some ringside observers thought the challenger, thirty-one, merited the victory but the contender endured the second defeat of his 28-bout professional journey.
Buatsi Claims Win in Slow Match
His career development has plateaued in the past few years through promotional disputes and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - possibly in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with both competitors willing to overcommit in a calculated opening few rounds.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after breaking his hand in the contest, was making just his second fight at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for Buatsi, who worked behind a protective stance to edge the cleaner periods.
The crowd's patience diminished because of regular grabbing, with the challenger slipping to the canvas several times during grappling.
Parker ended stronger, but several stanzas were challenging to assess. However, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just one round.
The victor progresses, but with the caliber of power puncher David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Hatton Homage Inspires Manchester Derby Contest
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a terrific Manchester vs Manchester contest to win the European light heavyweight belt.
The stadium fell silent for a profoundly moving tribute ahead of the contest as 10 bells rang in memory of Manchester's own Ricky Hatton, who died 46 years old in September.
It was the first major televised fight night in the urban center since Hatton's passing. As the final chime ended, the silence transitioned to a roar of "there's just one Hatton".
The fighting within the ring matched the sentiment. Arthur was sent to the canvas by a left hook squarely on the face in the second round, standing uncertainly to his feet on the referee's count.
But the traditional red attire of the fighter soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was marked up quickly, heavy swelling developing under his orbital area as the pair exchanged punishing blows.
Rea, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with effective uppercuts as the pace rarely dropped over the full distance.
The victor barely secured the result with judges scorecards of 114-114, close margin and 115-112, but the two athletes were relentless and courageous, all the qualities their inspiration Hatton stood for.
