UK light heavyweight Buatsi made a winning yet unimpressive debut to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a tight 10-round bout at the boxing arena.
But Parker landed significant shots, connecting with powerful clean blows in a match where the styles never quite clicked, with constant grabbing marring the contest.
The scoring judges had it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my greatest showing but what do champions do? They win," Buatsi commented in the ring as he was met by disapproval from the spectators.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a twentieth professional win.
Various analysts felt the challenger, 31, merited the victory but the Derbyshire fighter endured the second setback of his 28-bout professional journey.
The Champion Claims Victory in Dull Encounter
Buatsi's progress has slowed in recent times through promotional disputes and considerable time of inactivity.
Earlier forecast as the rising talent of British boxing, he now stands trying to fulfil that early promise - maybe in what seems like a final roll of the dice - under fresh management.
He began cautiously, with the two boxers willing to take risks in a tentative initial rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in 2022 after suffering a hand injury mid-fight, was competing in only his second appearance at light-heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for Buatsi, who operated with a tight guard to narrowly win the more effective periods.
The audience's tolerance wore thin amid frequent holding, with Parker going down multiple occasions during grappling.
The underdog finished the stronger, but several stanzas were challenging to assess. However, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
The victor moves on, but with the likes of heavy hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Homage Fuels Local Rivalry Fight
In the co-main event, Arthur defeated Rea by split-decision in a excellent Manchester vs Manchester fight to capture the European light-heavyweight belt.
The stadium became quiet for a profoundly moving memorial before the fight as ten bells tolled in honor of Manchester's own Ricky Hatton, who died aged 46 in September.
It was the initial significant broadcast fight night in the urban center since Hatton's death. As the last bell faded, the silence transitioned to a shout of "there's just one Hatton".
The fighting inside the ropes equaled the emotion. The eventual winner was knocked down by a powerful punch squarely on the jaw in the second round, rising shakily to his position on the count of eight.
But the traditional red equipment of Arthur soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was marked up soon, heavy swelling forming under his orbital area as the fighters exchanged hard punches.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace rarely dropped over twelve rounds.
The victor edged the result with judges scorecards of 114-114, narrow lead and clearer margin, but the two athletes were persistent and courageous, all the qualities their hero the legend embodied.
