UK light-heavyweight Buatsi made a winning yet underwhelming debut to life under new promoters with a points victory over Zach Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a majority decision in a close 10-round bout at the Manchester venue.
But Parker landed significant shots, delivering effective single shots in a match where the techniques didn't complement each other, with excessive holding disrupting the fight.
The officials had it 96-94 to Buatsi, with the third a even score.
"It wasn't my best display but what defines champions? They prevail," Buatsi commented in the ring as he was greeted with negative reactions from the audience.
The British fighter got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to secure a 20th pro success.
Various analysts felt the challenger, 31, should have been awarded the win but the contender experienced the second setback of his 28-fight career.
The Champion Secures Victory in Uneventful Match
His career development has plateaued in recent years through management issues and considerable time of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to achieve expectations - perhaps in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with the two boxers willing to take risks in a tentative early stages.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in two years ago after breaking his hand during the bout, was participating in his second bout at light heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for Buatsi, who utilized a protective stance to edge the better rounds.
The spectators' acceptance diminished during constant clinching, with Parker going down multiple occasions during grappling.
Parker ended stronger, but many rounds were challenging to assess. However, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for Parker, awarding Buatsi just only one stanza.
The victor advances, but with the presence of hard hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still appears challenging.
Hatton Tribute Fuels Local Rivalry Battle
In the supporting bout, Arthur beat Bradley Rea by divided decision in a terrific all-Manchester contest to capture the European light heavyweight title.
The stadium became quiet for a extremely emotional memorial before the fight as 10 bells tolled in honor of the city's native Ricky Hatton, who passed away at age 46 in September.
It was the premier televised match card in the urban center since Hatton's death. As the final chime disappeared, the stillness became a chant of "there's just one Hatton".
The action inside the ropes matched the feeling. Arthur was sent to the canvas by a left hook flush on the chin in the second round, getting up unsteadily to his footing on the referee's count.
But the Manchester United-red attire of the fighter soon pressed ahead again. From the other corner, Rea - in opposing blue - was injured early, noticeable damage appearing under his face as the duo landed hard punches.
Rea, 27, delivered effective strikes but Arthur, 34, matched the intensity with effective uppercuts as the pace hardly diminished over the full distance.
The victor edged the decision with official scores of draw, narrow lead and wider gap, but each competitor were relentless and full of heart, everything their inspiration Hatton embodied.
