British light heavyweight Buatsi secured a victory yet unimpressive debut to life 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 split decision in a competitive 10-round fight at the boxing arena.
But the challenger landed significant shots, connecting with powerful clean blows in a fight where the techniques failed to mesh, with frequent clinching marring the fight.
The officials had it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my finest performance but what do champions do? They succeed," the victor stated in the ringside as he was met by disapproval from the spectators.
The Londoner bounced back after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a 20th career victory.
Some ringside observers felt the challenger, 31, deserved the victory but the British boxer endured the second setback of his 28-fight professional journey.
Buatsi Earns Triumph in Uneventful Affair
The fighter's advancement has stalled in recent years through contract problems and extended periods of inactivity.
Earlier forecast as the rising talent of UK boxing, he now stands trying to realize his potential - possibly in what feels like a ultimate opportunity - under recent support.
He started carefully, with neither fighter prepared to overcommit in a cagey initial rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in two years ago after breaking his hand in the contest, was competing in only his second appearance at the higher weight class.
By the middle rounds, the underdog had made it competitive, causing problems for Buatsi, who operated with a solid defense to narrowly win the cleaner rounds.
The crowd's patience diminished amid constant clinching, with Parker going down various instances during grappling.
The underdog closed well, but multiple periods were difficult to score. However, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor progresses, but with the caliber of hard hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Hatton Tribute Inspires All-Manchester Fight
In the supporting bout, Arthur defeated Rea by close verdict in a outstanding local rivalry fight to win the European light-heavyweight title.
The stadium fell silent for a deeply poignant homage prior to the bout as a bell ceremony tolled in remembrance of Manchester's own Hatton, who passed away at age 46 in September.
It was the first major televised boxing event in the urban center since Hatton's death. As the final chime faded, the stillness transitioned to a shout of "there's just one Ricky Hatton".
The action during the bout matched the feeling. The eventual winner was floored by a significant blow flush on the jaw in the second round, standing uncertainly to his feet on the referee's count.
But the red-colored equipment of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was damaged early, noticeable damage developing under his face as the pair exchanged hard punches.
The challenger, 27, landed power punches but the champion, 34, responded in kind with effective uppercuts as the pace hardly diminished over 12 rounds.
Arthur barely secured the decision with judges scorecards of even score, narrow lead and clearer margin, but each competitor were persistent and full of heart, exactly what their hero the legend embodied.
