UK light-heavyweight Buatsi secured a victory yet unimpressive start to his career under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a split decision in a tight ten-round fight at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling clean blows in a contest where the approaches failed to mesh, with excessive holding disrupting the action.
The officials had it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my greatest showing but what do champions do? They prevail," the victor commented in the ring as he was faced boos from the audience.
The Londoner got back to winning after his maiden career setback - an epic battle with his previous opponent in last winter - to secure a twentieth professional win.
Various analysts thought the challenger, 31, deserved the win but the Derbyshire fighter endured the second loss of his 28-fight professional journey.
Buatsi Secures Triumph in Slow Encounter
The fighter's advancement has stalled in recent times through promotional disputes and extended periods of inactivity.
Once tipped as the next star of UK boxing, he now stands trying to achieve expectations - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter willing to take risks in a cagey early stages.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after suffering a hand injury in the contest, was making just his second bout at light-heavyweight.
By the halfway stage, the underdog had made it competitive, making life awkward for the favorite, who worked behind a solid defense to barely take the cleaner periods.
The spectators' acceptance decreased because of constant clinching, with Parker falling to the floor multiple occasions during close exchanges.
Parker finished the stronger, but several stanzas were hard to judge. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
The victor advances, but with the likes of power puncher Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - on this evidence - still appears challenging.
Hatton Memorial Fuels Manchester Derby Contest
In the secondary fight, Arthur overcame Bradley Rea by divided decision in a excellent all-Manchester contest to secure the European light-heavyweight championship.
The arena fell silent for a extremely emotional memorial ahead of the contest as 10 bells rang in memory of Manchester's own Ricky Hatton, who succumbed 46 years old in last month.
It was the premier televised match card in the city since Hatton's passing. As the last bell disappeared, the stillness transitioned to a chant of "only one Hatton".
The fighting inside the ropes reflected the emotion. The eventual winner was floored by a powerful punch squarely on the face in the initial stage, getting up unsteadily to his feet on the referee's count.
But the red-colored shorts of Arthur soon pressed ahead again. Across the ring, Rea - in competitive blue - was marked up quickly, noticeable damage forming under his orbital area as the pair exchanged punishing blows.
Rea, 27, connected with strong blows but Arthur, thirty-four, matched the intensity with stinging uppercuts as the pace seldom decreased over 12 rounds.
Arthur edged the decision with scoring tallies of even score, 115-113 and 115-112, but the two athletes were relentless and full of heart, everything their inspiration the legend represented.
