British light heavyweight Buatsi earned a win yet disappointing 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 seemingly secured him a majority decision in a close 10-round fight at the Co-op Live Arena.
But the challenger found success, delivering effective clean blows in a contest where the styles never quite clicked, with excessive holding disrupting the action.
Two judges scored it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my finest showing but what do champions do? They succeed," Buatsi said in the ringside as he was met by boos from the spectators.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to secure a twentieth professional win.
Several boxing experts believed the challenger, thirty-one, deserved the decision but the Derbyshire fighter suffered the second setback of his 28-match professional journey.
Buatsi Claims Triumph in Slow Encounter
Buatsi's progress has slowed in the past few years through contract problems and considerable time of inactivity.
Earlier forecast as the next star of British boxing, he now is positioned trying to achieve expectations - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors prepared to overcommit in a calculated early stages.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was making just his second appearance at the higher weight class.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who utilized a tight guard to edge the cleaner rounds.
The audience's tolerance diminished during regular grabbing, with the challenger slipping to the canvas various instances during close exchanges.
Parker finished the stronger, but many rounds were challenging to assess. Although, former world champion Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Hatton Memorial Motivates All-Manchester Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a terrific all-Manchester contest to win the European light-heavyweight title.
The arena grew hushed for a deeply poignant tribute ahead of the contest as ten bells tolled in memory of Manchester's own Ricky Hatton, who died aged 46 in September.
It was the premier televised match card in the urban center since the passing of Hatton. As the concluding sound faded, the silence became a chant of "there's just one Ricky Hatton".
The action within the ring matched the sentiment. Arthur was sent to the canvas by a left hook directly to the chin in the initial stage, standing uncertainly to his feet on the count of eight.
But the red-colored equipment of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was damaged early, heavy swelling appearing under his orbital area as the fighters exchanged punishing blows.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with effective uppercuts as the intensity rarely dropped over the full distance.
Arthur barely secured the verdict with judges scorecards of 114-114, close margin and 115-112, but each competitor were relentless and courageous, everything their idol the legend embodied.
