UK light-heavyweight Buatsi made a winning yet underwhelming beginning to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive ten-round bout at the Co-op Live Arena.
But the challenger found success, landing some telling clean blows in a match where the styles failed to mesh, with constant grabbing marring the action.
Two judges scored it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my greatest display but how do champions respond? They succeed," Buatsi said in the ring as he was met by disapproval from the spectators.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers believed the challenger, thirty-one, merited the win but the contender suffered the second defeat of his 28-bout professional journey.
The Champion Earns Triumph in Uneventful Affair
Buatsi's progress has plateaued in recent years through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of UK boxing, he now stands trying to realize his potential - maybe in what seems like a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers willing to be aggressive in a cagey opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent 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, the underdog had kept it close, causing problems for the favorite, who worked behind a protective stance to narrowly win the better stanzas.
The audience's tolerance wore thin during regular grabbing, with the challenger slipping to the canvas multiple occasions during grappling.
The underdog ended stronger, but several stanzas were hard to judge. However, previous titleholder the boxing analyst - commentating on Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
Buatsi progresses, but with the likes of power puncher Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Hatton Tribute Inspires Local Rivalry Contest
In the secondary fight, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding all-Manchester battle to secure the European light heavyweight belt.
The arena became quiet for a deeply poignant tribute ahead of the contest as ten bells tolled in memory of the city's native Hatton, who succumbed aged 46 in September.
It was the premier televised match card in the location since the passing of Hatton. As the last bell faded, the silence gave way to a shout of "there's only one Ricky Hatton".
The action within the ring equaled the sentiment. Arthur was sent to the canvas by a left hook squarely on the chin in the initial stage, rising shakily to his footing on the eight count.
But the Manchester United-red shorts of the fighter soon advanced again. Across the ring, Rea - in competitive blue - was marked up early, heavy swelling forming under his eye as the pair traded powerful shots.
Rea, twenty-seven, landed power punches but the champion, 34, matched the intensity with powerful upward punches as the pace hardly diminished over twelve rounds.
Arthur edged the verdict with judges scorecards of even score, narrow lead and clearer margin, but each competitor were determined and brave, all the qualities their idol Hatton embodied.
