UK light heavyweight Buatsi made a winning yet unimpressive debut to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a close 10-round bout at the Co-op Live Arena.
But Parker found success, landing some telling individual punches in a contest where the styles didn't complement each other, with frequent clinching disrupting the contest.
The scoring judges scored it 96-94 for to the winner, with the third a 95-95.
"It wasn't my greatest performance but what do champions do? They prevail," Buatsi said in the ring as he was met by boos from the spectators.
The Londoner bounced back after his first professional defeat - an epic battle with his previous opponent in last winter - to earn a twentieth professional win.
Several boxing experts believed the challenger, thirty-one, should have been awarded the victory but the contender endured the second setback of his 28-bout career.
The Champion Earns Win in Dull Encounter
Buatsi's progress has slowed in recent times through management issues and extended periods of lack of fights.
Previously predicted as the rising talent of UK boxing, he now finds himself trying to achieve expectations - possibly in what seems like a last chance - under recent support.
He started carefully, with neither fighter ready to be aggressive in a calculated initial rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after damaging his hand in the contest, was making just his second bout at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, causing problems for Buatsi, who utilized a tight guard to edge the better stanzas.
The spectators' acceptance decreased amid frequent holding, with the challenger falling to the floor multiple occasions during grappling.
Parker finished the stronger, but many rounds were difficult to score. However, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
The victor progresses, but with the caliber of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still appears challenging.
Hatton Memorial Fuels Manchester Derby Battle
In the co-main event, Lyndon Arthur beat Rea by divided decision in a excellent Manchester vs Manchester fight to capture the European light-heavyweight title.
The venue grew hushed for a deeply poignant memorial ahead of the contest as 10 bells rang in honor of the city's native Hatton, who succumbed 46 years old in recently.
It was the first major televised fight night in the city since Hatton's passing. As the final chime faded, the silence became a chant of "only one Hatton".
The action within the ring matched the emotion. The eventual winner was knocked down by a significant blow squarely on the jaw in the early round, rising shakily to his footing on the referee's count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. Across the ring, Rea - in rival City blue - was damaged quickly, heavy swelling developing under his face as the duo exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with effective uppercuts as the intensity hardly diminished over 12 rounds.
Arthur narrowly won the result with official scores of 114-114, narrow lead and 115-112, but each competitor were determined and courageous, all the qualities their idol the legend embodied.
