UK light-heavyweight Buatsi earned a win yet underwhelming start to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a judges' verdict in a competitive 10-round bout at the Manchester venue.
But the challenger landed significant shots, delivering effective clean blows in a contest where the styles never quite clicked, with excessive holding marring the fight.
The scoring judges had it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my greatest display but what defines champions? They prevail," the victor commented in the ringside as he was met by disapproval from the spectators.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in February - to secure a twentieth professional win.
Various analysts felt the challenger, thirty-one, should have been awarded the win but the British boxer suffered the second loss of his 28-match career.
The Champion Secures Win in Uneventful Affair
Buatsi's progress has stalled in the past few years through promotional disputes and considerable time of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to realize his potential - maybe in what feels like a ultimate opportunity - under recent support.
He started carefully, with neither fighter willing to overcommit in a cagey initial rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after breaking his hand in the contest, was making just his second fight at light heavyweight.
By the middle rounds, Parker had made it competitive, causing problems for the favorite, who operated with a tight guard to edge the better periods.
The crowd's patience diminished because of constant clinching, with the challenger going down several times during clinches.
The underdog ended stronger, but several stanzas were challenging to assess. Nevertheless, former world champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
Buatsi moves on, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Hatton Homage Fuels Local Rivalry Contest
In the secondary fight, Arthur defeated Bradley Rea by split-decision in a excellent all-Manchester fight to capture the European light-heavyweight belt.
The stadium fell silent for a profoundly moving tribute ahead of the contest as 10 bells rang in memory of Manchester's own Ricky Hatton, who succumbed at age 46 in last month.
It was the first major televised boxing event in the city since the passing of Hatton. As the concluding sound disappeared, the quiet gave way to a roar of "there's just one Hatton".
The fighting inside the ropes reflected the feeling. The eventual winner was knocked down by a left hook squarely on the jaw in the second round, getting up unsteadily to his feet on the eight count.
But the Manchester United-red shorts of Arthur soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was marked up early, noticeable damage forming under his eye as the duo exchanged hard punches.
The challenger, 27, landed power punches but Arthur, 34, matched the intensity with powerful upward punches as the pace rarely dropped over 12 rounds.
Arthur narrowly won the result with official scores of draw, narrow lead and wider gap, but the two athletes were determined and brave, everything their inspiration Hatton embodied.
