UK light heavyweight Buatsi made a winning yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a split decision in a competitive 10-round contest at the Manchester venue.
But Parker found success, connecting with powerful single shots in a match where the styles never quite clicked, with excessive holding disrupting the action.
Two judges had it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my greatest display but what do champions do? They succeed," Buatsi said in the ringside as he was met by boos from the spectators.
The British fighter bounced back after his maiden career setback - an thrilling contest with his previous opponent in last winter - to secure a 20th career victory.
Several boxing experts felt the challenger, 31, merited the decision but the contender experienced the second defeat of his 28-match professional journey.
Buatsi Claims Win in Uneventful Match
His career development has plateaued in recent years through contract problems and long spells of lack of fights.
Earlier forecast as the next star of British boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with neither fighter prepared to take risks in a cagey initial rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after damaging his hand during the bout, was competing in only his second bout at light-heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for the favorite, who utilized a solid defense to narrowly win the cleaner rounds.
The crowd's patience wore thin amid frequent holding, with the challenger falling to the floor multiple occasions during grappling.
The underdog finished the stronger, but many rounds were hard to judge. However, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, giving Buatsi just only one stanza.
Buatsi progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Hatton Homage Motivates Local Rivalry Contest
In the supporting bout, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific all-Manchester fight to secure the continental championship.
The arena became quiet for a profoundly moving tribute before the fight as ten bells rang in memory of Manchester's own Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the last bell disappeared, the quiet gave way to a roar of "there's only one Ricky Hatton".
The action inside the ropes reflected the emotion. The eventual winner was floored by a left hook squarely on the jaw in the second round, rising shakily to his feet on the eight count.
But the traditional red shorts of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was marked up early, noticeable damage appearing under his orbital area as the fighters exchanged punishing blows.
Rea, 27, landed power punches but the champion, 34, matched the intensity with stinging uppercuts as the action hardly diminished over twelve rounds.
Arthur narrowly won the decision with scoring tallies of draw, close margin and clearer margin, but each competitor were determined and courageous, everything their hero Hatton embodied.
