UK light heavyweight Buatsi earned a win yet unimpressive start to life 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 split decision in a competitive 10-round fight at the boxing arena.
But Parker landed significant shots, landing some telling single shots in a fight where the techniques never quite clicked, with constant grabbing spoiling the fight.
Two judges judged it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my best performance but what defines champions? They win," Buatsi commented in the ringside as he was greeted with boos from the spectators.
The Londoner got back to winning after his first professional defeat - an thrilling contest with Callum Smith in last winter - to earn a twentieth professional win.
Several boxing experts believed the challenger, 31, merited the win but the British boxer experienced the second setback of his 28-match career.
The Champion Earns Win in Uneventful Encounter
Buatsi's progress has stalled in recent times through management issues and long spells of lack of fights.
Previously predicted as the next star of British boxing, he now stands trying to fulfil that early promise - possibly in what appears to be a last chance - under fresh management.
He began cautiously, with the two boxers prepared to take risks in a cagey opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after damaging his hand in the contest, was making just his second bout at light-heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who worked behind a protective stance to edge the cleaner stanzas.
The crowd's patience decreased because of constant clinching, with Parker going down various instances during grappling.
The underdog closed well, but many rounds were hard to judge. Although, former world champion Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
The victor advances, but with the caliber of hard hitter David Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Hatton Tribute Fuels All-Manchester Fight
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a terrific local rivalry battle to secure the continental title.
The venue became quiet for a deeply poignant homage ahead of the contest as 10 bells sounded in remembrance of local hero Hatton, who died at age 46 in September.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the concluding sound ended, the stillness became a shout of "there's just one Hatton".
The competition within the ring reflected the sentiment. The eventual winner was floored by a significant blow squarely on the chin in the second round, standing uncertainly to his feet on the referee's count.
But the Manchester United-red attire of the fighter soon advanced again. Across the ring, the opponent - in opposing blue - was damaged early, noticeable damage forming under his face as the fighters traded hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with powerful upward punches as the pace rarely dropped over twelve rounds.
Arthur edged the verdict with official scores of even score, narrow lead and 115-112, but both fighters were persistent and full of heart, everything their idol the legend represented.
