UK light heavyweight Buatsi made a winning yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a split decision in a close ten-round contest at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful clean blows in a match where the styles failed to mesh, with excessive holding marring the action.
The scoring judges judged it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my best display but what do champions do? They succeed," Buatsi stated in the ringside as he was met by disapproval from the crowd.
The British fighter bounced back after his maiden career setback - an memorable fight with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers felt the challenger, thirty-one, deserved the victory but the British boxer suffered the second defeat of his 28-fight career.
Buatsi Secures Victory in Dull Match
Buatsi's progress has stalled in the past few years through management issues and considerable time of inactivity.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to realize his potential - maybe in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter willing to take risks in a tentative initial rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after suffering a hand injury during the bout, was competing in only his second appearance at the higher weight class.
By the middle rounds, Parker had kept it close, causing problems for Buatsi, who utilized a tight guard to narrowly win the cleaner stanzas.
The crowd's patience diminished because of constant clinching, with Parker going down several times during grappling.
The underdog ended stronger, but many rounds were challenging to assess. However, former world champion Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
Buatsi advances, but with the likes of power puncher Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
Hatton Memorial Inspires Manchester Derby Battle
In the supporting bout, Arthur overcame Rea by split-decision in a excellent local rivalry battle to secure the European light-heavyweight belt.
The stadium became quiet for a deeply poignant memorial ahead of the contest as 10 bells sounded in remembrance of Manchester's own Hatton, who succumbed 46 years old in last month.
It was the first major televised fight night in the city since Hatton's death. As the last bell disappeared, the quiet transitioned to a roar of "only one Hatton".
The competition within the ring matched the sentiment. Arthur was floored by a significant blow flush on the chin in the second round, getting up unsteadily to his footing on the eight count.
But the red-colored shorts of the fighter soon came forward again. On the opposite side, the opponent - in competitive blue - was damaged quickly, noticeable damage developing under his eye as the duo traded hard punches.
Rea, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with powerful upward punches as the action hardly diminished over twelve rounds.
Arthur narrowly won the verdict with official scores of draw, narrow lead and 115-112, but each competitor were determined and courageous, exactly what their inspiration Hatton embodied.
