British light-heavyweight Buatsi secured a victory yet disappointing debut to his career under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a tight 10-round fight at the boxing arena.
But the challenger had his moments, connecting with powerful clean blows in a match where the techniques didn't complement each other, with frequent clinching marring the action.
The scoring judges scored it 96-94 for to the winner, with the final judge a 95-95.
"It wasn't my greatest display but how do champions respond? They succeed," Buatsi said in the ring as he was met by negative reactions from the audience.
The Londoner got back to winning after his first professional defeat - an epic battle with Callum Smith in last winter - to earn a 20th career victory.
Several boxing experts thought the challenger, thirty-one, merited the victory but the British boxer suffered the second loss of his 28-match career.
Buatsi Claims Triumph in Slow Match
The fighter's advancement has stalled in recent years through contract problems and considerable time of inactivity.
Previously predicted as the future of UK boxing, he now stands trying to realize his potential - possibly in what feels like a last chance - under fresh management.
He started carefully, with neither fighter willing to overcommit in a calculated initial rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second fight at light-heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for the favorite, who operated with a protective stance to narrowly win the cleaner stanzas.
The crowd's patience decreased during constant clinching, with Parker falling to the floor multiple occasions during grappling.
The underdog finished the stronger, but many rounds were difficult to score. However, previous titleholder Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, awarding Buatsi just a single round.
Buatsi advances, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Homage Inspires Local Rivalry Contest
In the secondary fight, Arthur overcame Rea by divided decision in a outstanding Manchester vs Manchester fight to win the European light heavyweight title.
The arena fell silent for a profoundly moving memorial prior to the bout as a bell ceremony rang in remembrance of local hero Hatton, who passed away 46 years old in recently.
It was the premier televised match card in the city since Hatton's passing. As the last bell ended, the silence gave way to a shout of "there's just one Hatton".
The competition during the bout equaled the sentiment. The eventual winner was knocked down by a significant blow directly to the jaw in the second round, standing uncertainly to his footing on the eight count.
But the red-colored attire of the fighter soon advanced again. Across the ring, Rea - in opposing blue - was damaged early, noticeable damage appearing under his orbital area as the duo exchanged punishing blows.
The challenger, 27, connected with strong blows but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over twelve rounds.
The victor barely secured the decision with official scores of even score, 115-113 and 115-112, but both fighters were persistent and courageous, exactly what their idol Hatton represented.
