UK light heavyweight Buatsi secured a victory yet disappointing debut to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a judges' verdict in a tight ten-round contest at the Co-op Live Arena.
But Parker had his moments, delivering effective single shots in a match where the styles never quite clicked, with constant grabbing marring the action.
Two judges judged it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest display but what defines champions? They prevail," the victor commented in the ringside as he was greeted with negative reactions from the audience.
The Londoner bounced back after his initial pro loss - an epic battle with Callum Smith in February - to secure a 20th career victory.
Various analysts believed the challenger, 31, should have been awarded the decision but the contender endured the second defeat of his 28-fight career.
Buatsi Earns Win in Uneventful Encounter
Buatsi's progress has stalled in recent years through contract problems and long spells of inactivity.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to realize his potential - possibly in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with the two boxers ready to be aggressive in a tentative opening few rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second bout at the higher weight class.
By the halfway stage, Parker had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to edge the cleaner stanzas.
The audience's tolerance diminished during frequent holding, with Parker going down several times during close exchanges.
Parker finished the stronger, but many rounds were difficult to score. Nevertheless, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, giving Buatsi just only one stanza.
The victor progresses, but with the likes of heavy hitter David Benavidez, and Russian star Bivol leading the category, the path to championship success - judging by this showing - still seems difficult.
Hatton Tribute Fuels Local Rivalry Fight
In the secondary fight, Lyndon Arthur defeated Rea by split-decision in a outstanding local rivalry battle to secure the European light-heavyweight belt.
The arena fell silent for a deeply poignant tribute prior to the bout as a bell ceremony tolled in memory of local hero Hatton, who died at age 46 in last month.
It was the first major televised boxing event in the city since the passing of Hatton. As the last bell disappeared, the quiet gave way to a roar of "there's just one Hatton".
The competition inside the ropes reflected the sentiment. Arthur was floored by a significant blow squarely on the face in the initial stage, standing uncertainly to his feet on the referee's count.
But the traditional red shorts of Arthur soon came forward again. On the opposite side, the opponent - in competitive blue - was damaged quickly, noticeable damage appearing under his eye as the fighters exchanged powerful shots.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with powerful upward punches as the pace rarely dropped over the full distance.
The victor narrowly won the result with official scores of draw, narrow lead and clearer margin, but both fighters were determined and full of heart, all the qualities their idol the legend stood for.
