British light heavyweight Buatsi earned a win yet disappointing beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a split decision in a tight 10-round bout at the Manchester venue.
But Parker landed significant shots, landing some telling individual punches in a contest where the styles failed to mesh, with frequent clinching marring the fight.
The scoring judges scored it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best showing but what defines champions? They prevail," Buatsi said in the arena as he was faced disapproval from the audience.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in last winter - to earn a 20th career victory.
Various analysts believed the challenger, 31, merited the decision but the contender endured the second loss of his 28-bout professional journey.
Buatsi Secures Victory in Dull Affair
The fighter's advancement has slowed in recent times through promotional disputes and considerable time of inactivity.
Once tipped as the rising talent of UK boxing, he now stands trying to realize his potential - maybe in what seems like a last chance - under new promotional backing.
He opened tentatively, with the two boxers willing to be aggressive in a calculated opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was making just his second fight at light heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a protective stance to narrowly win the better stanzas.
The spectators' acceptance wore thin because of frequent holding, with Parker slipping to the canvas multiple occasions during close exchanges.
The underdog ended stronger, but many rounds were hard to judge. Nevertheless, ex-champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol leading the category, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Tribute Motivates Manchester Derby Contest
In the co-main event, Arthur beat Bradley Rea by divided decision in a terrific local rivalry battle to win the European light-heavyweight championship.
The venue grew hushed for a profoundly moving homage before the fight as 10 bells sounded in memory of local hero Hatton, who succumbed at age 46 in September.
It was the first major televised boxing event in the urban center since Hatton's passing. As the concluding sound faded, the silence transitioned to a chant of "only one Ricky Hatton".
The competition inside the ropes matched the feeling. The eventual winner was sent to the canvas by a left hook squarely on the face in the early round, getting up unsteadily to his position on the eight count.
But the Manchester United-red equipment of Arthur soon came forward again. On the opposite side, Rea - in opposing blue - was injured early, heavy swelling appearing under his face as the fighters traded powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with powerful upward punches as the intensity rarely dropped over twelve rounds.
The victor barely secured the decision with scoring tallies of 114-114, 115-113 and clearer margin, but each competitor were persistent and brave, everything their inspiration Hatton stood for.
