British light heavyweight Buatsi earned a win yet disappointing beginning to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a competitive 10-round bout at the Co-op Live Arena.
But the challenger had his moments, delivering effective single shots in a contest where the approaches didn't complement each other, with excessive holding spoiling the action.
The scoring judges had it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best display but what defines champions? They succeed," Buatsi stated in the arena as he was met by boos from the crowd.
The British fighter got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers felt the challenger, 31, should have been awarded the win but the Derbyshire fighter suffered the second loss of his 28-fight professional journey.
The Champion Earns Triumph in Dull Affair
Buatsi's progress has slowed in the past few years through contract problems and long spells of inactivity.
Earlier forecast as the rising talent of British boxing, he now is positioned trying to realize his potential - maybe in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with both competitors willing to take risks in a cagey initial rounds.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand mid-fight, was participating in his second bout at light-heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for the favorite, who worked behind a tight guard to edge the more effective stanzas.
The crowd's patience wore thin because of frequent holding, with Parker falling to the floor multiple occasions during close exchanges.
Parker closed well, but multiple periods were difficult to score. Nevertheless, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
Buatsi advances, but with the presence of heavy hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Memorial Fuels Local Rivalry Contest
In the supporting bout, Arthur overcame Rea by split-decision in a excellent Manchester vs Manchester fight to capture the European light-heavyweight championship.
The stadium fell silent for a deeply poignant homage ahead of the contest as ten bells tolled in honor of Manchester's own Ricky Hatton, who passed away aged 46 in September.
It was the premier televised boxing event in the urban center since Hatton's death. As the concluding sound faded, the silence gave way to a roar of "there's just one Hatton".
The competition inside the ropes reflected the sentiment. The eventual winner was floored by a left hook directly to the chin in the initial stage, getting up unsteadily to his position on the count of eight.
But the Manchester United-red equipment of the fighter soon pressed ahead again. Across the ring, Rea - in competitive blue - was damaged early, heavy swelling forming under his orbital area as the duo exchanged hard punches.
Rea, 27, connected with strong blows but Arthur, 34, matched the intensity with stinging uppercuts as the intensity hardly diminished over 12 rounds.
The victor barely secured the verdict with official scores of even score, 115-113 and wider gap, but the two athletes were persistent and courageous, exactly what their hero Hatton represented.
