UK light heavyweight Buatsi earned a win yet underwhelming beginning to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a close 10-round bout at the Manchester venue.
But Parker found success, delivering effective individual punches in a fight where the approaches failed to mesh, with frequent clinching spoiling the contest.
The scoring judges had it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my greatest display but how do champions respond? They succeed," Buatsi commented in the arena as he was faced disapproval from the crowd.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in last winter - to secure a twentieth professional win.
Several boxing experts felt Parker, thirty-one, merited the victory but the contender suffered the second setback of his 28-bout career.
Buatsi Secures Victory in Uneventful Encounter
His career development has plateaued in the past few years through contract problems and long spells of lack of fights.
Previously predicted as the future of British boxing, he now finds himself trying to realize his potential - perhaps in what seems like a last chance - under fresh management.
He opened tentatively, with both competitors ready to take risks in a cagey initial rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was competing in only his second bout at light heavyweight.
By the middle rounds, the underdog had made it competitive, making life awkward for Buatsi, who worked behind a tight guard to barely take the cleaner periods.
The audience's tolerance diminished during frequent holding, with Parker going down various instances during close exchanges.
Parker closed well, but many rounds were hard to judge. However, previous titleholder Carl Frampton - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the likes of hard hitter David Benavidez, and Russian star Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Hatton Homage Inspires Manchester Derby Battle
In the co-main event, Lyndon Arthur beat Rea by divided decision in a excellent all-Manchester battle to secure the European light-heavyweight title.
The venue grew hushed for a extremely emotional tribute ahead of the contest as 10 bells tolled in memory of local hero Hatton, who passed away aged 46 in last month.
It was the premier televised match card in the city since the passing of Hatton. As the concluding sound disappeared, the stillness became a chant of "there's just one Ricky Hatton".
The competition inside the ropes matched the feeling. The eventual winner was floored by a powerful punch flush on the face in the initial stage, rising shakily to his footing on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was injured early, heavy swelling forming under his orbital area as the fighters traded powerful shots.
The challenger, 27, landed power punches but the champion, thirty-four, responded in kind with powerful upward punches as the intensity rarely dropped over the full distance.
The victor edged the verdict with official scores of 114-114, 115-113 and 115-112, but each competitor were relentless and brave, exactly what their inspiration the legend stood for.
