UK light-heavyweight Buatsi secured a victory yet unimpressive debut 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 competitive ten-round fight at the Co-op Live Arena.
But Parker found success, delivering effective clean blows in a match where the approaches didn't complement each other, with frequent clinching disrupting the fight.
The scoring judges scored it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best display but what do champions do? They prevail," Buatsi stated in the ringside as he was met by negative reactions from the spectators.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts felt Parker, thirty-one, should have been awarded the win but the British boxer experienced the second setback of his 28-bout career.
Buatsi Claims Win in Dull Match
Buatsi's progress has plateaued in recent times through contract problems and long spells of inactivity.
Once tipped as the next star of British boxing, he now is positioned trying to realize his potential - possibly in what feels like a final roll of the dice - under recent support.
He opened tentatively, with the two boxers willing to overcommit in a cagey early stages.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after breaking his hand during the bout, was participating in his second appearance at light heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to narrowly win the more effective stanzas.
The crowd's patience decreased during regular grabbing, with Parker going down various instances during grappling.
The underdog finished the stronger, but several stanzas were hard to judge. Nevertheless, previous titleholder the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
Buatsi progresses, but with the likes of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
Hatton Memorial Inspires Manchester Derby Fight
In the secondary fight, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding all-Manchester battle to win the European light-heavyweight championship.
The stadium grew hushed for a profoundly moving homage prior to the bout as 10 bells sounded in honor of Manchester's own Ricky Hatton, who passed away 46 years old in September.
It was the first major televised match card in the urban center since Hatton's passing. As the final chime ended, the silence transitioned to a chant of "there's just one Hatton".
The fighting during the bout reflected the emotion. Arthur was knocked down by a left hook squarely on the jaw in the early round, rising shakily to his position on the count of eight.
But the Manchester United-red shorts of the fighter soon pressed ahead again. Across the ring, Rea - in rival City blue - was damaged early, noticeable damage forming under his orbital area as the fighters landed hard punches.
Rea, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the action hardly diminished over 12 rounds.
The victor narrowly won the decision with judges scorecards of 114-114, close margin and clearer margin, but the two athletes were determined and courageous, everything their idol the legend embodied.
