British light-heavyweight Buatsi secured a victory yet underwhelming beginning to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a close 10-round bout at the Manchester venue.
But Parker found success, connecting with powerful individual punches in a contest where the approaches didn't complement each other, with frequent clinching disrupting the action.
The officials had it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my best showing but how do champions respond? They prevail," Buatsi stated in the ring as he was met by negative reactions from the spectators.
The Londoner bounced back after his initial pro loss - an epic battle with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers thought the challenger, 31, deserved the win but the British boxer endured the second loss of his 28-fight professional journey.
Buatsi Claims Win in Slow Match
The fighter's advancement has stalled in recent times through management issues and considerable time of inactivity.
Once tipped as the next star of UK boxing, he now is positioned trying to realize his potential - perhaps in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers willing to overcommit in a tentative early stages.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was making just his second fight at light heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for the favorite, who operated with a tight guard to barely take the cleaner stanzas.
The crowd's patience wore thin during regular grabbing, with the challenger slipping to the canvas multiple occasions during grappling.
Parker ended stronger, but several stanzas were hard to judge. Nevertheless, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for the challenger, giving Buatsi just a single round.
The victor progresses, but with the caliber of hard hitter Benavidez, and Russian champion Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Hatton Homage Motivates Local Rivalry Battle
In the co-main event, Lyndon Arthur defeated Rea by divided decision in a outstanding local rivalry battle to win the European light-heavyweight belt.
The arena grew hushed for a profoundly moving tribute before the fight as 10 bells sounded in honor of the city's native Hatton, who died 46 years old in September.
It was the initial significant broadcast match card in the city since the passing of Hatton. As the final chime faded, the stillness transitioned to a chant of "there's only one Ricky Hatton".
The action inside the ropes matched the feeling. The eventual winner was knocked down by a powerful punch directly to the face in the second round, rising shakily to his footing on the eight count.
But the traditional red attire of the fighter soon came forward again. Across the ring, the opponent - in competitive blue - was marked up quickly, noticeable damage forming under his eye as the duo traded punishing blows.
The challenger, 27, connected with strong blows but the champion, thirty-four, responded in kind with stinging uppercuts as the action hardly diminished over twelve rounds.
Arthur edged the result with official scores of even score, narrow lead and clearer margin, but both fighters were persistent and courageous, exactly what their idol Hatton stood for.
