British light-heavyweight Buatsi earned a win yet underwhelming beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a competitive ten-round bout at the Co-op Live Arena.
But Parker had his moments, connecting with powerful single shots in a fight where the techniques never quite clicked, with constant grabbing spoiling the contest.
The scoring judges scored it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest display but what defines champions? They prevail," the victor stated in the ring as he was greeted with negative reactions from the crowd.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Various analysts thought Parker, thirty-one, merited the decision but the British boxer suffered the second loss of his 28-bout career.
The Champion Earns Victory in Slow Match
His career development has stalled in the past few years through management issues and long spells of lack of fights.
Previously predicted as the next star of British boxing, he now stands trying to realize his potential - maybe in what seems like a ultimate opportunity - under new promotional backing.
He opened tentatively, with neither fighter prepared to be aggressive in a cagey initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury in the contest, was competing in only his second appearance at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for Buatsi, who worked behind a protective stance to narrowly win the cleaner stanzas.
The spectators' acceptance decreased amid frequent holding, with the challenger falling to the floor various instances during clinches.
Parker finished the stronger, but many rounds were hard to judge. However, former world champion the boxing analyst - commentating on Dazn - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor progresses, but with the caliber of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Tribute Fuels Manchester Derby Contest
In the co-main event, Arthur overcame Rea by split-decision in a outstanding all-Manchester fight to secure the European light-heavyweight title.
The venue fell silent for a profoundly moving tribute before the fight as 10 bells tolled in remembrance of the city's native Ricky Hatton, who died at age 46 in September.
It was the premier televised boxing event in the location since the passing of Hatton. As the final chime ended, the stillness gave way to a chant of "there's only one Hatton".
The action inside the ropes equaled the emotion. Arthur was sent to the canvas by a significant blow squarely on the chin in the early round, standing uncertainly to his footing on the count of eight.
But the Manchester United-red equipment of the fighter soon pressed ahead again. Across the ring, Rea - in competitive blue - was injured soon, significant bruising developing under his orbital area as the duo traded hard punches.
The challenger, 27, landed power punches but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace seldom decreased over the full distance.
The victor edged the decision with judges scorecards of draw, close margin and wider gap, but each competitor were determined and brave, exactly what their idol Hatton embodied.
