UK light-heavyweight Buatsi earned a win yet unimpressive debut to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a close ten-round contest at the boxing arena.
But the challenger landed significant shots, landing some telling individual punches in a fight where the approaches didn't complement each other, with constant grabbing spoiling the contest.
The officials had it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my best display but what do champions do? They win," Buatsi commented in the ringside as he was faced negative reactions from the spectators.
The British fighter got back to winning after his initial pro loss - an epic battle with Callum Smith in February - to earn a 20th career victory.
Various analysts thought the challenger, thirty-one, should have been awarded the victory but the British boxer suffered the second loss of his 28-fight professional journey.
Buatsi Secures Triumph in Uneventful Match
Buatsi's progress has plateaued in the past few years through promotional disputes and long spells of lack of fights.
Earlier forecast as the next star of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under recent support.
He began cautiously, with neither fighter prepared to take risks in a calculated early stages.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second bout at light-heavyweight.
By the middle rounds, Parker had stayed in contention, making life awkward for Buatsi, who worked behind a protective stance to edge the better stanzas.
The audience's tolerance decreased amid frequent holding, with Parker falling to the floor various instances during grappling.
Parker finished the stronger, but several stanzas were hard to judge. Nevertheless, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
Buatsi advances, but with the caliber of power puncher David Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Hatton Memorial Inspires Local Rivalry Fight
In the supporting bout, Lyndon Arthur beat Rea by divided decision in a terrific all-Manchester fight to capture the continental championship.
The stadium fell silent for a deeply poignant memorial ahead of the contest as a bell ceremony sounded in honor of the city's native Hatton, who succumbed 46 years old in recently.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the final chime ended, the stillness became a roar of "there's just one Ricky Hatton".
The action within the ring matched the emotion. Arthur was sent to the canvas by a powerful punch directly to the jaw in the second round, getting up unsteadily to his footing on the count of eight.
But the red-colored shorts of Arthur soon came forward again. Across the ring, Rea - in opposing blue - was injured quickly, noticeable damage appearing under his orbital area as the pair landed punishing blows.
Rea, 27, connected with strong blows but the champion, 34, matched the intensity with stinging uppercuts as the pace rarely dropped over 12 rounds.
Arthur narrowly won the decision with official scores of draw, narrow lead and 115-112, but each competitor were determined and brave, exactly what their idol the legend embodied.
