UK light-heavyweight Buatsi earned a win yet underwhelming debut 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 tight ten-round bout at the Co-op Live Arena.
But Parker found success, delivering effective individual punches in a match where the styles never quite clicked, with excessive holding disrupting the fight.
Two judges had it 96-94 in favor to the winner, with the third a even score.
"It wasn't my finest performance but what defines champions? They succeed," Buatsi said in the ring as he was greeted with negative reactions from the spectators.
The British fighter bounced back after his first professional defeat - an memorable fight with his previous opponent in last winter - to secure a 20th pro success.
Various analysts thought the challenger, 31, should have been awarded the win but the contender experienced the second loss of his 28-match career.
Buatsi Earns Triumph in Slow Match
His career development has slowed in the past few years through contract problems and extended periods of inactivity.
Previously predicted as the future of British boxing, he now is positioned trying to fulfil that early promise - maybe in what seems like a final roll of the dice - under recent support.
He started carefully, with both competitors willing to be aggressive in a calculated initial rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after damaging his hand during the bout, was making just his second bout at the higher weight class.
By the middle rounds, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a protective stance to narrowly win the better periods.
The spectators' acceptance wore thin because of frequent holding, with the challenger slipping to the canvas several times during close exchanges.
The underdog closed well, but many rounds were hard to judge. However, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the likes of hard hitter David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Fuels All-Manchester Contest
In the secondary fight, Arthur defeated Bradley Rea by close verdict in a excellent all-Manchester battle to capture the continental belt.
The venue fell silent for a deeply poignant tribute ahead of the contest as a bell ceremony sounded in memory of Manchester's own Hatton, who succumbed at age 46 in recently.
It was the premier televised fight night in the city since Hatton's death. As the final chime faded, the quiet transitioned to a roar of "only one Ricky Hatton".
The action inside the ropes equaled the sentiment. Arthur was sent to the canvas by a powerful punch directly to the chin in the early round, rising shakily to his feet on the eight count.
But the traditional red shorts of the fighter soon advanced again. Across the ring, Rea - in rival City blue - was damaged soon, significant bruising forming under his orbital area as the fighters traded punishing blows.
The challenger, 27, connected with strong blows but the champion, thirty-four, fought fire with fire with powerful upward punches as the action hardly diminished over the full distance.
Arthur barely secured the decision with judges scorecards of 114-114, 115-113 and wider gap, but each competitor were persistent and full of heart, exactly what their idol the legend embodied.
