UK light heavyweight Buatsi secured a victory yet underwhelming start to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a close ten-round bout at the Co-op Live Arena.
But Parker found success, delivering effective single shots in a contest where the approaches failed to mesh, with excessive holding disrupting the action.
The scoring judges scored it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my greatest performance but what do champions do? They win," the victor said in the ring as he was greeted with disapproval from the spectators.
The British fighter bounced back after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a twentieth professional win.
Some ringside observers believed Parker, thirty-one, should have been awarded the win but the contender experienced the second setback of his 28-bout professional journey.
The Champion Earns Victory in Slow Match
His career development has plateaued in the past few years through promotional disputes and considerable time of lack of fights.
Earlier forecast as the next star of UK boxing, he now finds himself trying to realize his potential - maybe in what seems like a last chance - under recent support.
He started carefully, with the two boxers prepared to overcommit in a tentative early stages.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was competing in only his second bout at light-heavyweight.
By the halfway stage, Parker had stayed in contention, creating difficulties for Buatsi, who worked behind a protective stance to barely take the better rounds.
The spectators' acceptance diminished amid frequent holding, with Parker falling to the floor multiple occasions during clinches.
The underdog ended stronger, but multiple periods were challenging to assess. Nevertheless, previous titleholder the boxing analyst - working with Dazn - had it strongly leaning for Parker, giving Buatsi just only one stanza.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Russian champion Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Hatton Homage Motivates Manchester Derby Contest
In the supporting bout, Lyndon Arthur overcame Rea by divided decision in a outstanding local rivalry contest to secure the European light heavyweight belt.
The stadium fell silent for a extremely emotional memorial prior to the bout as 10 bells rang in honor of Manchester's own Ricky Hatton, who died 46 years old in last month.
It was the premier televised fight night in the city since Hatton's passing. As the final chime disappeared, the quiet transitioned to a chant of "only one Ricky Hatton".
The competition inside the ropes equaled the feeling. Arthur was knocked down by a left hook directly to the face in the initial stage, rising shakily to his feet on the count of eight.
But the red-colored equipment of the fighter soon advanced again. From the other corner, Rea - in rival City blue - was damaged quickly, significant bruising forming under his eye as the duo landed hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with stinging uppercuts as the pace hardly diminished over twelve rounds.
The victor barely secured the result with official scores of draw, close margin and 115-112, but the two athletes were persistent and full of heart, all the qualities their idol Hatton stood for.
