UK light heavyweight Buatsi earned a win yet disappointing debut to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a majority decision in a tight 10-round contest at the Manchester venue.
But the challenger found success, delivering effective individual punches in a contest where the styles never quite clicked, with excessive holding marring the contest.
Two judges scored it 96-94 to the winner, with the third a even score.
"It wasn't my greatest showing but what do champions do? They prevail," the victor stated in the arena as he was faced boos from the crowd.
The Londoner got back to winning after his initial pro loss - an epic battle with his previous opponent in February - to secure a 20th career victory.
Some ringside observers felt the challenger, thirty-one, merited the victory but the British boxer endured the second setback of his 28-match professional journey.
Buatsi Claims Win in Uneventful Affair
The fighter's advancement has plateaued in recent times through contract problems and long spells of inactivity.
Earlier forecast as the next star of British boxing, he now stands trying to realize his potential - maybe in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter ready to overcommit in a calculated opening few rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after breaking his hand during the bout, was participating in his second bout at the higher weight class.
By the halfway stage, the underdog had stayed in contention, causing problems for Buatsi, who worked behind a tight guard to narrowly win the more effective periods.
The audience's tolerance decreased because of frequent holding, with Parker falling to the floor several times during close exchanges.
Parker closed well, but many rounds were challenging to assess. Nevertheless, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, awarding Buatsi just one round.
Buatsi moves on, but with the likes of hard hitter David Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Homage Fuels Manchester Derby Fight
In the secondary fight, Lyndon Arthur beat Bradley Rea by split-decision in a excellent local rivalry battle to secure the European light heavyweight championship.
The stadium fell silent for a deeply poignant memorial prior to the bout as a bell ceremony rang in remembrance of the city's native Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the concluding sound faded, the stillness became a shout of "only one Hatton".
The fighting within the ring equaled the emotion. The eventual winner was knocked down by a significant blow squarely on the chin in the initial stage, standing uncertainly to his position on the referee's count.
But the Manchester United-red shorts of Arthur soon advanced again. Across the ring, the opponent - in opposing blue - was injured soon, heavy swelling developing under his face as the pair landed punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with stinging uppercuts as the intensity hardly diminished over twelve rounds.
The victor barely secured the result with scoring tallies of draw, 115-113 and 115-112, but the two athletes were determined and courageous, exactly what their idol the legend represented.
