British light-heavyweight Buatsi secured a victory yet unimpressive beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a close 10-round bout at the boxing arena.
But the challenger landed significant shots, connecting with powerful single shots in a contest where the styles didn't complement each other, with constant grabbing spoiling the contest.
The scoring judges scored it 96-94 for to the winner, with the third a 95-95.
"It wasn't my greatest performance but what do champions do? They prevail," Buatsi stated in the ringside as he was faced boos from the spectators.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Various analysts felt the challenger, 31, merited the decision but the British boxer experienced the second loss of his 28-bout career.
Buatsi Earns Victory in Slow Encounter
His career development has slowed in recent times through contract problems and long spells of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter ready to be aggressive in a calculated early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was competing in only his second appearance at light-heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who worked behind a protective stance to edge the better rounds.
The crowd's patience diminished because of frequent holding, with Parker slipping to the canvas various instances during grappling.
The underdog closed well, but several stanzas were hard to judge. However, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, giving Buatsi just a single round.
The victor moves on, but with the likes of heavy hitter Benavidez, and Russian champion Bivol ruling the division, the road to world glory - based on this performance - still seems difficult.
Hatton Tribute Inspires Local Rivalry Battle
In the co-main event, Arthur overcame Rea by split-decision in a outstanding all-Manchester contest to secure the European light heavyweight belt.
The venue fell silent for a deeply poignant homage ahead of the contest as a bell ceremony rang in memory of the city's native Hatton, who passed away at age 46 in recently.
It was the premier televised boxing event in the location since Hatton's death. As the final chime faded, the quiet became a roar of "only one Hatton".
The fighting within the ring reflected the emotion. The eventual winner was floored by a left hook squarely on the chin in the second round, rising shakily to his feet on the eight count.
But the red-colored equipment of the fighter soon came forward again. From the other corner, Rea - in competitive blue - was damaged early, heavy swelling forming under his eye as the pair landed punishing blows.
The challenger, 27, landed power punches but the champion, 34, matched the intensity with effective uppercuts as the pace rarely dropped over the full distance.
The victor narrowly won the verdict with scoring tallies of 114-114, close margin and clearer margin, but the two athletes were determined and courageous, all the qualities their hero Hatton represented.
