British light heavyweight Buatsi secured a victory yet unimpressive debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a tight 10-round contest at the Manchester venue.
But Parker had his moments, connecting with powerful individual punches in a contest where the techniques didn't complement each other, with constant grabbing marring the fight.
The officials scored it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest performance but what do champions do? They prevail," Buatsi commented in the ring as he was faced negative reactions from the crowd.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in last winter - to secure a 20th pro success.
Various analysts felt the challenger, thirty-one, should have been awarded the victory but the Derbyshire fighter experienced the second loss of his 28-match professional journey.
Buatsi Claims Win in Slow Encounter
Buatsi's progress has slowed in recent times through contract problems and extended periods of inactivity.
Earlier forecast as the next star of British boxing, he now stands trying to realize his potential - possibly in what seems like a last chance - under recent support.
He opened tentatively, with both competitors ready to be aggressive in a cagey early stages.
Parker, whose single earlier setback 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 fight at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for the favorite, who utilized a tight guard to barely take the better rounds.
The spectators' acceptance diminished amid constant clinching, with the challenger going down several times during clinches.
The underdog finished the stronger, but many rounds were difficult to score. Although, former world champion Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the caliber of hard hitter David Benavidez, and Russian star Bivol leading the category, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Memorial Fuels Local Rivalry Battle
In the co-main event, Lyndon Arthur overcame Rea by split-decision in a terrific all-Manchester battle to capture the European light heavyweight title.
The arena became quiet for a profoundly moving tribute before the fight as a bell ceremony rang in honor of Manchester's own Hatton, who passed away 46 years old in last month.
It was the first major televised match card in the location since Hatton's death. As the final chime disappeared, the silence gave way to a roar of "only one Hatton".
The action inside the ropes equaled the sentiment. The eventual winner was sent to the canvas by a significant blow flush on the face in the initial stage, standing uncertainly to his position on the referee's count.
But the traditional red shorts of the fighter soon advanced again. Across the ring, Rea - in competitive blue - was damaged soon, significant bruising appearing under his face as the fighters exchanged punishing blows.
Rea, 27, connected with strong blows but the champion, 34, responded in kind with effective uppercuts as the action rarely dropped over twelve rounds.
The victor narrowly won the decision with official scores of draw, close margin and wider gap, but each competitor were persistent and brave, everything their idol the legend represented.
