UK light-heavyweight Buatsi earned a win yet disappointing start to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a competitive 10-round contest at the Co-op Live Arena.
But the challenger found success, connecting with powerful individual punches in a fight where the approaches never quite clicked, with constant grabbing disrupting the action.
Two judges had it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my best showing but what do champions do? They succeed," Buatsi commented in the ringside as he was met by boos from the crowd.
The British fighter got back to winning after his maiden career setback - an epic battle with his previous opponent in last winter - to earn a 20th pro success.
Some ringside observers believed the challenger, 31, deserved the victory but the Derbyshire fighter endured the second defeat of his 28-match career.
The Champion Earns Win in Slow Affair
The fighter's advancement has stalled in recent times through promotional disputes and extended periods of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to realize his potential - maybe in what feels like a last chance - under recent support.
He began cautiously, with the two boxers prepared to take risks in a tentative opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand in the contest, was participating in his second appearance at the higher weight class.
By the halfway stage, Parker had kept it close, causing problems for Buatsi, who utilized a solid defense to narrowly win the cleaner periods.
The spectators' acceptance decreased during regular grabbing, with Parker falling to the floor various instances during grappling.
The underdog finished the stronger, but many rounds were challenging to assess. Although, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, giving Buatsi just one round.
Buatsi progresses, but with the likes of hard hitter Benavidez, and Russian star Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Hatton Memorial Motivates Manchester Derby Fight
In the secondary fight, Arthur overcame Bradley Rea by close verdict in a outstanding local rivalry battle to win the European light heavyweight title.
The arena grew hushed for a profoundly moving homage ahead of the contest as a bell ceremony tolled in remembrance of local hero Ricky Hatton, who passed away 46 years old in September.
It was the first major televised fight night in the urban center since Hatton's passing. As the concluding sound ended, the stillness became a shout of "there's only one Ricky Hatton".
The competition within the ring equaled the feeling. The eventual winner was knocked down by a left hook flush on the face in the early round, standing uncertainly to his position on the count of eight.
But the Manchester United-red shorts of Arthur soon advanced again. From the other corner, the opponent - in competitive blue - was injured soon, heavy swelling forming under his orbital area as the duo exchanged punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with stinging uppercuts as the pace rarely dropped over 12 rounds.
The victor edged the decision with scoring tallies of 114-114, 115-113 and 115-112, but each competitor were determined and brave, exactly what their idol the legend embodied.
