UK light heavyweight Buatsi earned a win yet disappointing debut to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a tight 10-round fight at the Manchester venue.
But Parker found success, landing some telling individual punches in a contest where the techniques didn't complement each other, with excessive holding marring the fight.
Two judges judged it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They succeed," the victor said in the arena as he was greeted with disapproval from the audience.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in February - to secure a 20th career victory.
Several boxing experts believed Parker, thirty-one, should have been awarded the win but the contender suffered the second setback of his 28-fight career.
Buatsi Earns Triumph in Dull Affair
Buatsi's progress has stalled in the past few years through promotional disputes and long spells of inactivity.
Previously predicted as the next star of British boxing, he now finds himself trying to achieve expectations - perhaps in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers ready to take risks in a cagey opening few rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after damaging his hand during the bout, was competing in only his second appearance at the higher weight class.
By the halfway stage, Parker had made it competitive, creating difficulties for the favorite, who worked behind a solid defense to barely take the better periods.
The spectators' acceptance wore thin because of regular grabbing, with Parker going down various instances during grappling.
The underdog ended stronger, but multiple periods were challenging to assess. Nevertheless, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, awarding Buatsi just one round.
Buatsi advances, but with the caliber of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Hatton Memorial Inspires Manchester Derby Battle
In the supporting bout, Arthur overcame Bradley Rea by split-decision in a excellent all-Manchester fight to capture the European light-heavyweight championship.
The stadium became quiet for a profoundly moving memorial ahead of the contest as a bell ceremony rang in remembrance of the city's native Ricky Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast boxing event in the urban center since Hatton's death. As the concluding sound faded, the stillness transitioned to a roar of "only one Hatton".
The fighting within the ring equaled the feeling. The eventual winner was knocked down by a powerful punch flush on the jaw in the second round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red attire of Arthur soon came forward again. On the opposite side, the opponent - in rival City blue - was damaged quickly, significant bruising appearing under his orbital area as the duo exchanged powerful shots.
Rea, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the action hardly diminished over twelve rounds.
The victor barely secured the result with judges scorecards of draw, narrow lead and 115-112, but each competitor were relentless and brave, all the qualities their hero Hatton embodied.
