UK light heavyweight Buatsi made a winning yet disappointing start to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a split decision in a tight ten-round bout at the Manchester venue.
But Parker landed significant shots, connecting with powerful single shots in a contest where the techniques didn't complement each other, with constant grabbing marring the contest.
Two judges scored it 96-94 to Buatsi, with the third a even score.
"It wasn't my greatest showing but what do champions do? They prevail," Buatsi commented in the arena as he was greeted with boos from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to earn a twentieth professional win.
Various analysts felt Parker, thirty-one, deserved the win but the British boxer endured the second loss of his 28-match professional journey.
Buatsi Claims Win in Uneventful Encounter
His career development has plateaued in recent years through contract problems and extended periods of inactivity.
Once tipped as the future of British boxing, he now finds himself trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under recent support.
He started carefully, with both competitors ready to overcommit in a cagey initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was competing in only his second fight at light heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for the favorite, who utilized a solid defense to narrowly win the better rounds.
The crowd's patience diminished during frequent holding, with the challenger slipping to the canvas multiple occasions during clinches.
The underdog closed well, but several stanzas were difficult to score. However, previous titleholder Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
Buatsi moves on, but with the caliber of hard hitter David Benavidez, and Russian star Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Hatton Tribute Fuels Manchester Derby Contest
In the supporting bout, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific local rivalry contest to capture the European light-heavyweight title.
The stadium became quiet for a profoundly moving tribute before the fight as a bell ceremony sounded in honor of Manchester's own Hatton, who succumbed at age 46 in recently.
It was the first major televised boxing event in the city since the passing of Hatton. As the concluding sound faded, the stillness became a shout of "there's only one Ricky Hatton".
The competition during the bout matched the feeling. The eventual winner was floored by a left hook flush on the chin in the initial stage, rising shakily to his feet on the count of eight.
But the red-colored shorts of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was injured soon, significant bruising developing under his eye as the fighters landed powerful shots.
Rea, twenty-seven, 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 verdict with official scores of even score, close margin and 115-112, but the two athletes were relentless and courageous, everything their idol the legend represented.
