British light-heavyweight Buatsi made a winning yet underwhelming start to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a majority decision in a tight 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 approaches didn't complement each other, with frequent clinching spoiling the action.
The scoring judges had it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my greatest display but what do champions do? They prevail," Buatsi said in the ringside as he was met by disapproval from the spectators.
The Londoner bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to earn a twentieth professional win.
Some ringside observers felt Parker, thirty-one, deserved the victory but the contender endured the second setback of his 28-fight professional journey.
The Champion Secures Victory in Uneventful Affair
Buatsi's progress has plateaued in recent years through management issues and long spells of inactivity.
Previously predicted as the future of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what feels like a last chance - under fresh management.
He started carefully, with both competitors 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 damaging his hand during the bout, was competing in only his second appearance at the higher weight class.
By the middle rounds, Parker had kept it close, creating difficulties for the favorite, who utilized a protective stance to edge the cleaner periods.
The spectators' acceptance wore thin amid frequent holding, with Parker slipping to the canvas several times during grappling.
Parker closed well, but several stanzas were difficult to score. However, previous titleholder Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, giving Buatsi just a single round.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still appears challenging.
Hatton Memorial Fuels All-Manchester Fight
In the supporting bout, Lyndon Arthur defeated Bradley Rea by close verdict in a excellent local rivalry fight to capture the European light-heavyweight title.
The stadium fell silent for a extremely emotional memorial before the fight as a bell ceremony rang in honor of local hero Ricky Hatton, who succumbed 46 years old in September.
It was the first major televised fight night in the location since Hatton's passing. As the last bell disappeared, the silence gave way to a roar of "there's only one Hatton".
The action during the bout matched the emotion. The eventual winner was floored by a left hook directly to the chin in the early round, standing uncertainly to his feet on the eight count.
But the traditional red attire of Arthur soon came forward again. Across the ring, Rea - in opposing blue - was marked up quickly, noticeable damage forming under his eye as the duo traded powerful shots.
Rea, 27, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur edged the verdict with judges scorecards of 114-114, close margin and 115-112, but each competitor were relentless and full of heart, exactly what their idol Hatton stood for.
