British light-heavyweight Buatsi secured a victory yet disappointing beginning to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a tight ten-round contest at the Co-op Live Arena.
But the challenger had his moments, landing some telling individual punches in a match where the techniques never quite clicked, with frequent clinching spoiling the fight.
The scoring judges judged it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest showing but how do champions respond? They prevail," Buatsi stated in the arena as he was faced boos from the spectators.
The British fighter got back to winning after his first professional defeat - an thrilling contest with Callum Smith in February - to secure a 20th pro success.
Some ringside observers believed Parker, thirty-one, merited the victory but the Derbyshire fighter endured the second loss of his 28-bout professional journey.
The Champion Secures Win in Uneventful Affair
Buatsi's progress has stalled in the past few years through promotional disputes and extended periods of inactivity.
Once tipped as the next star of UK boxing, he now stands trying to realize his potential - maybe in what seems like a last chance - under fresh management.
He started carefully, with both competitors ready to take risks in a cagey initial rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was participating in his second bout at the higher weight class.
By the middle rounds, Parker had made it competitive, causing problems for the favorite, who operated with a solid defense to barely take the cleaner rounds.
The crowd's patience wore thin amid regular grabbing, with the challenger going down various instances during grappling.
Parker closed well, but multiple periods were difficult to score. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, scoring for Buatsi just a single round.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Russian star Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Hatton Homage Fuels Manchester Derby Fight
In the co-main event, Lyndon Arthur defeated Bradley Rea by divided decision in a excellent all-Manchester battle to capture the European light heavyweight title.
The stadium became quiet for a profoundly moving tribute before the fight as 10 bells tolled in remembrance of Manchester's own Hatton, who died at age 46 in September.
It was the first major televised fight night in the urban center since the passing of Hatton. As the concluding sound ended, the stillness gave way to a chant of "there's only one Ricky Hatton".
The action during the bout matched the sentiment. The eventual winner was knocked down by a significant blow flush on the face in the second round, getting up unsteadily to his position on the referee's count.
But the traditional red attire of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was damaged soon, noticeable damage appearing under his eye as the duo traded hard punches.
Rea, 27, delivered effective strikes but Arthur, 34, responded in kind with stinging uppercuts as the pace rarely dropped over 12 rounds.
The victor edged the verdict with official scores of draw, narrow lead and wider gap, but both fighters were determined and courageous, all the qualities their idol Hatton embodied.
