UK light heavyweight Buatsi made a winning yet unimpressive start to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a split decision in a competitive ten-round contest at the Co-op Live Arena.
But Parker had his moments, connecting with powerful clean blows in a fight where the approaches failed to mesh, with constant grabbing disrupting the contest.
The officials had it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my best showing but how do champions respond? They win," Buatsi commented in the ring as he was greeted with negative reactions from the audience.
The British fighter bounced back after his maiden career setback - an thrilling contest with Callum Smith in last winter - to claim a 20th career victory.
Some ringside observers felt the challenger, 31, deserved the decision but the contender experienced the second defeat of his 28-match career.
Buatsi Earns Triumph in Dull Match
His career development has slowed in recent years through promotional disputes and considerable time of lack of fights.
Previously predicted as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a last chance - under fresh management.
He opened tentatively, with the two boxers prepared to overcommit in a tentative initial rounds.
Parker, whose only previous defeat 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 fight at the higher weight class.
By the middle rounds, the underdog had kept it close, making life awkward for the favorite, who operated with a solid defense to narrowly win the cleaner stanzas.
The audience's tolerance wore thin because of frequent holding, with the challenger slipping to the canvas various instances during close exchanges.
The underdog finished the stronger, but many rounds were challenging to assess. Nevertheless, former world champion Carl Frampton - commentating on Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
Buatsi progresses, but with the caliber of heavy hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Tribute Inspires Local Rivalry Battle
In the co-main event, Arthur beat Bradley Rea by split-decision in a outstanding all-Manchester contest to capture the European light heavyweight belt.
The arena fell silent for a extremely emotional memorial prior to the bout as 10 bells tolled in remembrance of the city's native Ricky Hatton, who succumbed at age 46 in September.
It was the first major televised boxing event in the urban center since Hatton's passing. As the concluding sound ended, the silence transitioned to a roar of "only one Hatton".
The competition during the bout matched the emotion. The eventual winner was sent to the canvas by a left hook flush on the chin in the early round, rising shakily to his feet on the eight count.
But the red-colored equipment of Arthur soon pressed ahead again. On the opposite side, Rea - in competitive blue - was marked up quickly, heavy swelling developing under his face as the fighters traded hard punches.
The challenger, 27, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the pace rarely dropped over 12 rounds.
The victor barely secured the result with judges scorecards of even score, narrow lead and clearer margin, but the two athletes were persistent and brave, all the qualities their inspiration Hatton represented.
