British light heavyweight Buatsi earned a win yet unimpressive beginning to life under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a close 10-round contest at the Manchester venue.
But the challenger landed significant shots, landing some telling individual punches in a contest where the techniques failed to mesh, with excessive holding disrupting the fight.
The officials scored it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best display but how do champions respond? They succeed," Buatsi stated in the ringside as he was faced negative reactions from the spectators.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to secure a 20th career victory.
Several boxing experts thought the challenger, 31, should have been awarded the decision but the Derbyshire fighter endured the second defeat of his 28-match professional journey.
Buatsi Earns Triumph in Slow Affair
Buatsi's progress has plateaued in recent times through management issues and long spells of lack of fights.
Previously predicted as the future of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a last chance - under fresh management.
He opened tentatively, with both competitors prepared to take risks in a cagey early stages.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after breaking his hand in the contest, was competing in only his second appearance at light heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for the favorite, who operated with a protective stance to edge the more effective periods.
The audience's tolerance diminished amid frequent holding, with the challenger going down various instances during close exchanges.
The underdog closed well, but several stanzas were hard to judge. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
The victor advances, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
Hatton Homage Fuels Manchester Derby Contest
In the supporting bout, Arthur defeated Rea by split-decision in a outstanding local rivalry fight to secure the European light-heavyweight championship.
The arena became quiet for a deeply poignant memorial before the fight as 10 bells tolled in remembrance of the city's native Ricky Hatton, who died aged 46 in last month.
It was the first major televised fight night in the city since the passing of Hatton. As the final chime disappeared, the quiet gave way to a shout of "only one Hatton".
The competition inside the ropes equaled the emotion. Arthur was knocked down by a powerful punch flush on the chin in the initial stage, getting up unsteadily to his position on the count of eight.
But the red-colored equipment of Arthur soon came forward again. Across the ring, Rea - in opposing blue - was damaged quickly, noticeable damage appearing under his eye as the duo landed powerful shots.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with stinging uppercuts as the pace rarely dropped over twelve rounds.
The victor narrowly won the verdict with scoring tallies of draw, close margin and 115-112, but both fighters were persistent and full of heart, everything their inspiration Hatton embodied.
