British light heavyweight Buatsi made a winning yet disappointing debut to his career under fresh promotional backing with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a tight 10-round contest at the Manchester venue.
But Parker had his moments, delivering effective clean blows in a match where the styles failed to mesh, with excessive holding disrupting the fight.
The officials scored it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my finest showing but how do champions respond? They prevail," Buatsi stated in the ring as he was greeted with disapproval from the spectators.
The Londoner got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a 20th pro success.
Various analysts felt Parker, 31, deserved the victory but the contender suffered the second loss of his 28-bout career.
The Champion Earns Victory in Dull Encounter
His career development has stalled in recent times through promotional disputes and long spells of inactivity.
Once tipped as the next star of British boxing, he now stands trying to achieve expectations - perhaps in what feels like a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers ready to take risks in a cagey early stages.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second fight at the higher weight class.
By the halfway stage, Parker had stayed in contention, causing problems for the favorite, who worked behind a solid defense to barely take the cleaner periods.
The crowd's patience decreased during constant clinching, with the challenger slipping to the canvas various instances during grappling.
The underdog closed well, but multiple periods were challenging to assess. Nevertheless, former world champion the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, awarding Buatsi just only one stanza.
Buatsi progresses, but with the presence of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
Hatton Tribute Motivates Manchester Derby Contest
In the secondary fight, Lyndon Arthur defeated Rea by divided decision in a excellent all-Manchester fight to capture the European light heavyweight belt.
The arena became quiet for a deeply poignant homage before the fight as a bell ceremony tolled in memory of local hero Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the concluding sound ended, the stillness gave way to a chant of "only one Ricky Hatton".
The fighting inside the ropes matched the emotion. The eventual winner was sent to the canvas by a significant blow flush on the jaw in the early round, rising shakily to his footing on the count of eight.
But the traditional red shorts of the fighter soon advanced again. Across the ring, Rea - in rival City blue - was damaged soon, heavy swelling appearing under his eye as the duo exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with effective uppercuts as the action rarely dropped over twelve rounds.
Arthur barely secured the verdict with judges scorecards of 114-114, narrow lead and clearer margin, but the two athletes were relentless and full of heart, everything their inspiration Hatton stood for.
