British light heavyweight Buatsi secured a victory yet disappointing start to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a tight 10-round bout at the boxing arena.
But Parker had his moments, landing some telling individual punches in a contest where the styles didn't complement each other, with frequent clinching marring the action.
Two judges had it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my greatest performance but what do champions do? They prevail," Buatsi commented in the ring as he was met by disapproval from the audience.
The British fighter returned to winning ways after his first professional defeat - an epic battle with Callum Smith in last winter - to earn a twentieth professional win.
Various analysts felt the challenger, thirty-one, deserved the victory but the Derbyshire fighter suffered the second loss of his 28-fight career.
Buatsi Claims Victory in Uneventful Match
His career development has stalled in recent times through contract problems and extended periods of inactivity.
Earlier forecast as the rising talent of British boxing, he now is positioned trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with neither fighter prepared to take risks in a cagey opening few rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after breaking his hand in the contest, was participating in his second fight at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, causing problems for the favorite, who worked behind a tight guard to edge the better rounds.
The spectators' acceptance diminished during frequent holding, with Parker going down several times during grappling.
The underdog ended stronger, but several stanzas were hard to judge. Nevertheless, previous titleholder Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just one round.
The victor advances, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Memorial Inspires Manchester Derby Contest
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a excellent all-Manchester fight to secure the European light heavyweight title.
The stadium grew hushed for a profoundly moving homage prior to the bout as 10 bells tolled in remembrance of the city's native Hatton, who died at age 46 in last month.
It was the first major televised boxing event in the city since Hatton's death. As the final chime disappeared, the stillness transitioned to a roar of "there's only one Ricky Hatton".
The fighting within the ring reflected the feeling. Arthur was sent to the canvas by a significant blow directly to the chin in the early round, standing uncertainly to his footing on the eight count.
But the traditional red shorts of the fighter soon pressed ahead again. Across the ring, Rea - in opposing blue - was marked up quickly, heavy swelling developing under his orbital area as the pair exchanged punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with stinging uppercuts as the intensity seldom decreased over twelve rounds.
Arthur edged the verdict with judges scorecards of even score, narrow lead and 115-112, but the two athletes were persistent and brave, exactly what their hero the legend represented.
