British light-heavyweight Buatsi earned a win yet disappointing debut to life under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a tight 10-round bout at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful single shots in a match where the approaches never quite clicked, with frequent clinching disrupting the action.
The scoring judges had it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my best performance but how do champions respond? They prevail," Buatsi said in the ringside as he was met by negative reactions from the audience.
The Londoner returned to winning ways after his first professional defeat - an epic battle with Callum Smith in February - to secure a twentieth professional win.
Some ringside observers believed the challenger, 31, merited the victory but the Derbyshire fighter endured the second loss of his 28-match professional journey.
Buatsi Claims Victory in Uneventful Affair
Buatsi's progress has plateaued in recent times 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 fulfil that early promise - possibly in what feels like a ultimate opportunity - under fresh management.
He began cautiously, with both competitors prepared to overcommit in a cagey early stages.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was participating in his second appearance at light heavyweight.
By the fight's midpoint, the underdog had kept it close, causing problems for the favorite, who operated with a solid defense to barely take the more effective stanzas.
The audience's tolerance decreased because of frequent holding, with the challenger going down various instances during grappling.
Parker closed well, but several stanzas were difficult to score. However, former world champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, scoring for Buatsi just a single round.
Buatsi moves on, but with the caliber of power puncher David Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Tribute Fuels Manchester Derby Fight
In the secondary fight, Lyndon Arthur overcame Rea by split-decision in a outstanding local rivalry contest to capture the continental championship.
The venue became quiet for a profoundly moving memorial prior to the bout as ten bells rang in memory of the city's native Ricky Hatton, who died aged 46 in recently.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the final chime faded, the stillness became a chant of "there's just one Hatton".
The action within the ring matched the feeling. The eventual winner was sent to the canvas by a significant blow flush on the chin in the early round, rising shakily to his feet on the referee's count.
But the Manchester United-red shorts of the fighter soon came forward again. Across the ring, the opponent - in rival City blue - was injured early, significant bruising appearing under his face as the duo exchanged hard punches.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with powerful upward punches as the action seldom decreased over twelve rounds.
The victor barely secured the verdict with official scores of even score, close margin and 115-112, but each competitor were persistent and full of heart, exactly what their hero the legend stood for.
