UK light-heavyweight Buatsi secured a victory yet unimpressive beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a competitive 10-round bout at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful individual punches in a contest where the techniques failed to mesh, with frequent clinching spoiling the action.
The scoring judges had it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my greatest showing but how do champions respond? They win," Buatsi commented in the arena as he was greeted with boos from the crowd.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Some ringside observers thought the challenger, thirty-one, merited the win but the British boxer endured the second setback of his 28-bout career.
Buatsi Earns Triumph in Uneventful Affair
The fighter's advancement has slowed in the past few years through contract problems and considerable time of lack of fights.
Earlier forecast as the next star of the British fight scene, he now is positioned trying to achieve expectations - possibly in what feels like a final roll of the dice - under fresh management.
He began cautiously, with both competitors prepared to overcommit in a calculated initial rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after breaking his hand mid-fight, was competing in only his second appearance at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for Buatsi, who operated with a tight guard to barely take the more effective rounds.
The audience's tolerance wore thin during frequent holding, with the challenger falling to the floor various instances during close exchanges.
The underdog closed well, but several stanzas were hard to judge. Although, former world champion Carl Frampton - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
The victor moves on, but with the presence of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Memorial Inspires Local Rivalry Battle
In the secondary fight, Arthur defeated Bradley Rea by close verdict in a terrific all-Manchester fight to secure the European light-heavyweight title.
The venue became quiet for a profoundly moving memorial before the fight as 10 bells sounded in memory of Manchester's own Ricky Hatton, who succumbed aged 46 in September.
It was the first major televised boxing event in the city since Hatton's death. As the final chime faded, the silence became a chant of "there's just one Ricky Hatton".
The action within the ring matched the emotion. The eventual winner was knocked down by a significant blow squarely on the jaw in the initial stage, standing uncertainly to his footing on the eight count.
But the traditional red equipment of Arthur soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was marked up soon, significant bruising developing under his eye as the fighters traded hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with stinging uppercuts as the intensity hardly diminished over 12 rounds.
Arthur narrowly won the decision with official scores of draw, close margin and wider gap, but the two athletes were persistent and brave, everything their hero Hatton stood for.
