British light-heavyweight Buatsi secured a victory yet underwhelming start to life under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a tight 10-round fight at the Manchester venue.
But the challenger had his moments, delivering effective single shots in a match where the styles didn't complement each other, with frequent clinching spoiling the contest.
The scoring judges judged it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest showing but what do champions do? They win," the victor commented in the ring as he was met by boos from the audience.
The British fighter returned to winning ways after his first professional defeat - an epic battle with his previous opponent in last winter - to secure a 20th pro success.
Several boxing experts thought Parker, 31, should have been awarded the decision but the British boxer suffered the second defeat of his 28-match career.
Buatsi Earns Win in Uneventful Affair
Buatsi's progress has stalled in recent years through contract problems and long spells of inactivity.
Once tipped as the rising talent of British boxing, he now finds himself trying to achieve expectations - possibly in what seems like a final roll of the dice - under fresh management.
He started carefully, with neither fighter ready to overcommit in a cagey opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after suffering a hand injury during the bout, was competing in only his second bout at the higher weight class.
By the halfway stage, the underdog had made it competitive, causing problems for the favorite, who utilized a tight guard to narrowly win the cleaner rounds.
The crowd's patience decreased amid constant clinching, with Parker falling to the floor various instances during clinches.
Parker ended stronger, but many rounds were challenging to assess. However, previous titleholder the boxing analyst - commentating on Dazn - had it particularly wide for Parker, giving Buatsi just one round.
The victor moves on, but with the likes of hard hitter Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Homage Motivates Manchester Derby Contest
In the co-main event, Arthur beat Rea by divided decision in a terrific local rivalry battle to capture the continental championship.
The stadium became quiet for a deeply poignant memorial ahead of the contest as ten bells tolled in remembrance of Manchester's own Hatton, who passed away aged 46 in September.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the last bell ended, the quiet became a shout of "there's just one Ricky Hatton".
The fighting within the ring equaled the emotion. Arthur was knocked down by a significant blow squarely on the face in the initial stage, rising shakily to his position on the eight count.
But the Manchester United-red shorts of the fighter soon advanced again. On the opposite side, the opponent - in rival City blue - was damaged soon, heavy swelling developing under his face as the pair exchanged punishing blows.
The challenger, 27, delivered effective strikes but Arthur, 34, matched the intensity with effective uppercuts as the intensity hardly diminished over the full distance.
The victor edged the decision with judges scorecards of 114-114, 115-113 and 115-112, but both fighters were relentless and brave, everything their inspiration Hatton stood for.
