British light-heavyweight Buatsi earned a win yet disappointing debut to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a split decision in a tight ten-round contest at the boxing arena.
But Parker landed significant shots, landing some telling clean blows in a match where the approaches failed to mesh, with constant grabbing marring the contest.
The officials had it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my finest display but what do champions do? They succeed," the victor said in the ringside as he was greeted with negative reactions from the crowd.
The Londoner bounced back after his initial pro loss - an thrilling contest with his previous opponent in last winter - to earn a 20th pro success.
Several boxing experts thought the challenger, thirty-one, deserved the victory but the contender suffered the second setback of his 28-fight career.
Buatsi Secures Win in Uneventful Encounter
Buatsi's progress has slowed in recent years through promotional disputes and considerable time of inactivity.
Earlier forecast as the next star of UK boxing, he now stands trying to fulfil that early promise - possibly in what feels like a final roll of the dice - under recent support.
He started carefully, with the two boxers ready to be aggressive in a tentative initial rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was competing in only his second bout at the higher weight class.
By the middle rounds, the underdog had stayed in contention, causing problems for Buatsi, who operated with a tight guard to barely take the better periods.
The spectators' acceptance diminished amid constant clinching, with Parker falling to the floor multiple occasions during clinches.
The underdog ended stronger, but many rounds were difficult to score. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, giving Buatsi just a single round.
Buatsi advances, but with the presence of hard hitter David Benavidez, and Russian champion Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Memorial Inspires All-Manchester Fight
In the co-main event, Arthur defeated Rea by close verdict in a terrific local rivalry contest to win the European light-heavyweight championship.
The stadium grew hushed for a extremely emotional homage prior to the bout as 10 bells sounded in honor of the city's native Ricky Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast fight night in the city since Hatton's death. As the final chime disappeared, the quiet became a shout of "only one Ricky Hatton".
The fighting within the ring reflected the sentiment. The eventual winner was knocked down by a powerful punch directly to the chin in the early round, standing uncertainly to his feet on the count of eight.
But the Manchester United-red shorts of Arthur soon pressed ahead again. Across the ring, Rea - in rival City blue - was injured quickly, significant bruising forming under his eye as the pair traded hard punches.
The challenger, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with effective uppercuts as the intensity hardly diminished over 12 rounds.
Arthur edged the verdict with judges scorecards of even score, close margin and 115-112, but each competitor were persistent and full of heart, everything their inspiration Hatton represented.
