British light heavyweight Buatsi earned a win yet underwhelming start to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a split decision in a tight ten-round fight at the boxing arena.
But Parker had his moments, delivering effective clean blows in a fight where the styles never quite clicked, with constant grabbing spoiling the fight.
The officials scored it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest showing but what defines champions? They prevail," Buatsi said in the ringside as he was faced disapproval from the audience.
The Londoner bounced back after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a twentieth professional win.
Some ringside observers felt the challenger, 31, should have been awarded the decision but the Derbyshire fighter suffered the second setback of his 28-fight professional journey.
The Champion Secures Triumph in Dull Match
His career development has slowed in recent times through contract problems and considerable time of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now finds himself trying to realize his potential - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He opened tentatively, with both competitors prepared to take risks in a calculated early stages.
Parker, whose only previous defeat came at super middleweight against his former opponent in two years ago after damaging his hand during the bout, was making just his second fight at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for the favorite, who utilized a solid defense to edge the better rounds.
The spectators' acceptance wore thin amid constant clinching, with the challenger slipping to the canvas various instances during grappling.
Parker closed well, but many rounds were hard to judge. However, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the caliber of hard hitter David Benavidez, and Russian star Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Hatton Tribute Fuels Local Rivalry Fight
In the co-main event, Arthur beat Bradley Rea by split-decision in a outstanding local rivalry battle to capture the European light-heavyweight championship.
The stadium became quiet for a deeply poignant memorial prior to the bout as 10 bells rang in memory of local hero Ricky Hatton, who died 46 years old in September.
It was the first major televised match card in the urban center since Hatton's passing. As the final chime disappeared, the stillness became a shout of "there's just one Hatton".
The competition within the ring equaled the feeling. The eventual winner was floored by a left hook squarely on the chin in the initial stage, standing uncertainly to his footing on the eight count.
But the traditional red shorts of Arthur soon advanced again. On the opposite side, Rea - in competitive blue - was damaged soon, heavy swelling appearing under his face as the duo landed powerful shots.
The challenger, twenty-seven, connected with strong blows but the champion, 34, responded in kind with powerful upward punches as the pace rarely dropped over twelve rounds.
Arthur barely secured the result with official scores of even score, close margin and 115-112, but each competitor were relentless and brave, exactly what their hero the legend embodied.
