British light-heavyweight Buatsi earned a win yet disappointing start to life under recent management 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 ten-round bout at the boxing arena.
But Parker found success, connecting with powerful single shots in a match where the styles failed to mesh, with excessive holding spoiling the contest.
Two judges judged it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my greatest showing but what do champions do? They win," Buatsi stated in the arena as he was faced boos from the spectators.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in last winter - to secure a 20th career victory.
Various analysts thought the challenger, thirty-one, merited the victory but the contender endured the second loss of his 28-match career.
The Champion Earns Victory in Dull Encounter
Buatsi's progress has slowed in the past few years through promotional disputes and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to achieve expectations - perhaps in what seems like a final roll of the dice - under recent support.
He opened tentatively, with both competitors ready to overcommit in a calculated early stages.
The challenger, whose sole prior loss 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, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a protective stance to edge the more effective rounds.
The audience's tolerance wore thin because of regular grabbing, with the challenger slipping to the canvas various instances during close exchanges.
Parker closed well, but many rounds were hard to judge. However, ex-champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for Parker, giving Buatsi just one round.
Buatsi advances, but with the likes of hard hitter Benavidez, and Russian star Bivol ruling the division, the road to world glory - on this evidence - still appears challenging.
Hatton Homage Inspires Local Rivalry Battle
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding local rivalry contest to secure the continental belt.
The arena grew hushed for a extremely emotional memorial ahead of the contest as a bell ceremony sounded in remembrance of Manchester's own Ricky Hatton, who died 46 years old in last month.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the final chime faded, the stillness became a roar of "only one Ricky Hatton".
The competition within the ring reflected the emotion. Arthur was knocked down by a powerful punch flush on the jaw in the early round, getting up unsteadily to his position on the eight count.
But the red-colored attire of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was damaged early, significant bruising appearing under his face as the fighters traded punishing blows.
The challenger, 27, delivered effective strikes but Arthur, 34, matched the intensity with effective uppercuts as the intensity rarely dropped over the full distance.
The victor edged the decision with scoring tallies of even score, close margin and clearer margin, but the two athletes were relentless and courageous, all the qualities their idol Hatton embodied.
