UK light-heavyweight Buatsi secured a victory yet underwhelming start to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a tight 10-round contest at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling single shots in a fight where the styles failed to mesh, with excessive holding spoiling the action.
The scoring judges had it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my finest display but how do champions respond? They succeed," Buatsi said in the ringside as he was met by disapproval from the crowd.
The Londoner got back to winning after his first professional defeat - an epic battle with Callum Smith in February - to secure a 20th pro success.
Several boxing experts felt Parker, thirty-one, merited the victory but the contender experienced the second loss of his 28-match professional journey.
Buatsi Earns Win in Uneventful Match
His career development has stalled in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of British boxing, he now stands trying to achieve expectations - possibly in what seems like a last chance - under new promotional backing.
He began cautiously, with both competitors ready to be aggressive in a tentative early stages.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand during the bout, was competing in only his second appearance at light-heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for the favorite, who operated with a tight guard to edge the cleaner stanzas.
The spectators' acceptance decreased because of regular grabbing, with the challenger going down several times during close exchanges.
The underdog finished the stronger, but many rounds were challenging to assess. However, former world champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just a single round.
Buatsi progresses, but with the caliber of hard hitter Benavidez, and Russian champion Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Hatton Tribute Fuels Manchester Derby Contest
In the secondary fight, Arthur beat Bradley Rea by split-decision in a outstanding Manchester vs Manchester contest to win the European light-heavyweight championship.
The arena fell silent for a extremely emotional homage prior to the bout as 10 bells tolled in honor of Manchester's own Ricky Hatton, who succumbed aged 46 in September.
It was the premier televised fight night in the urban center since the passing of Hatton. As the concluding sound faded, the quiet gave way to a roar of "there's only one Ricky Hatton".
The fighting during the bout matched the emotion. Arthur was floored by a powerful punch flush on the jaw in the early round, rising shakily to his footing on the eight count.
But the traditional red shorts of Arthur soon pressed ahead again. On the opposite side, Rea - in competitive blue - was damaged early, significant bruising developing under his face as the fighters traded hard punches.
Rea, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity rarely dropped over 12 rounds.
The victor narrowly won the result with judges scorecards of draw, narrow lead and clearer margin, but the two athletes were persistent and courageous, everything their idol Hatton represented.
