UK light-heavyweight Buatsi secured a victory yet disappointing start to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's work rate likely gained him a judges' verdict in a tight ten-round fight at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful single shots in a contest where the approaches didn't complement each other, with excessive holding disrupting the contest.
The scoring judges scored it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my best performance but what defines champions? They prevail," the victor said in the ringside as he was greeted with disapproval from the audience.
The British fighter bounced back after his maiden career setback - an memorable fight with his previous opponent in last winter - to secure a twentieth professional win.
Some ringside observers felt the challenger, 31, merited the win but the British boxer endured the second loss of his 28-match career.
Buatsi Claims Victory in Slow Match
Buatsi's progress has slowed in recent years through management issues and long spells of inactivity.
Earlier forecast as the future of the British fight scene, he now is positioned trying to realize his potential - possibly in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with the two boxers willing to take risks in a calculated opening few rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after breaking his hand in the contest, was competing in only his second appearance at light-heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who operated with a protective stance to narrowly win the cleaner stanzas.
The crowd's patience diminished amid constant clinching, with Parker falling to the floor various instances during clinches.
The underdog closed well, but multiple periods were challenging to assess. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just one round.
Buatsi moves on, but with the likes of power puncher Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Hatton Tribute Fuels Local Rivalry Contest
In the co-main event, Arthur overcame Rea by divided decision in a excellent local rivalry fight to capture the European light-heavyweight belt.
The venue fell silent for a deeply poignant homage before the fight as ten bells rang in honor of local hero Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the final chime faded, the stillness became a shout of "there's only one Ricky Hatton".
The competition within the ring reflected the sentiment. Arthur was knocked down by a powerful punch directly to the face in the second round, rising shakily to his position on the count of eight.
But the Manchester United-red equipment of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was injured soon, significant bruising developing under his orbital area as the fighters traded punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with effective uppercuts as the pace seldom decreased over 12 rounds.
The victor narrowly won the decision with judges scorecards of even score, close margin and 115-112, but each competitor were determined and full of heart, exactly what their inspiration the legend represented.
