British light-heavyweight Buatsi earned a win yet disappointing debut to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a competitive 10-round contest at the boxing arena.
But Parker found success, connecting with powerful clean blows in a contest where the techniques didn't complement each other, with frequent clinching spoiling the contest.
The officials had it 96-94 to the winner, with the third a 95-95.
"It wasn't my finest showing but how do champions respond? They prevail," the victor said in the ringside as he was met by boos from the spectators.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to claim a 20th pro success.
Some ringside observers felt Parker, thirty-one, merited the victory but the British boxer experienced the second setback of his 28-fight professional journey.
Buatsi Earns Victory in Dull Affair
His career development has stalled in recent times through promotional disputes and considerable time of inactivity.
Previously predicted as the next star of the British fight scene, he now stands trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter ready to be aggressive in a cagey early stages.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was competing in only his second bout at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who worked behind a protective stance to edge the more effective rounds.
The crowd's patience decreased during constant clinching, with the challenger going down multiple occasions during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. Nevertheless, former world champion Carl Frampton - working with Dazn - had it significantly in favor for Parker, giving Buatsi just one round.
Buatsi advances, but with the likes of heavy hitter Benavidez, and Russian star Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Hatton Homage Inspires Local Rivalry Fight
In the co-main event, Arthur overcame Rea by close verdict in a excellent all-Manchester contest to win the European light heavyweight title.
The stadium became quiet for a profoundly moving homage prior to the bout as ten bells tolled in memory of Manchester's own Hatton, who died aged 46 in last month.
It was the first major televised match card in the city since the passing of Hatton. As the concluding sound faded, the stillness transitioned to a roar of "only one Ricky Hatton".
The action inside the ropes matched the sentiment. The eventual winner was knocked down by a left hook squarely on the jaw in the second round, rising shakily to his position on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. From the other corner, Rea - in competitive blue - was damaged quickly, heavy swelling forming under his orbital area as the pair exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with stinging uppercuts as the pace rarely dropped over twelve rounds.
Arthur barely secured the result with scoring tallies of draw, 115-113 and clearer margin, but the two athletes were determined and brave, exactly what their hero the legend embodied.
