British light heavyweight Buatsi secured a victory yet underwhelming beginning to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a split decision in a competitive ten-round fight at the Manchester venue.
But Parker found success, connecting with powerful individual punches in a match where the techniques didn't complement each other, with constant grabbing spoiling the action.
Two judges scored it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my greatest showing but what defines champions? They succeed," Buatsi commented in the ring as he was greeted with disapproval from the spectators.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Various analysts thought Parker, 31, deserved the win but the contender experienced the second defeat of his 28-match career.
The Champion Secures Victory in Uneventful Encounter
His career development has plateaued in recent years through management issues and considerable time of inactivity.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to realize his potential - maybe in what feels like a last chance - under new promotional backing.
He started carefully, with both competitors ready to be aggressive in a tentative initial rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was participating in his second appearance at light-heavyweight.
By the halfway stage, Parker had kept it close, causing problems for the favorite, who operated with a tight guard to barely take the more effective rounds.
The audience's tolerance diminished during constant clinching, with the challenger slipping to the canvas several times during close exchanges.
The underdog closed well, but several stanzas were hard to judge. However, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
Buatsi advances, but with the likes of power puncher Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - on this evidence - still looks steep.
Hatton Memorial Fuels All-Manchester Fight
In the co-main event, Arthur overcame Rea by close verdict in a terrific Manchester vs Manchester battle to capture the European light heavyweight title.
The stadium grew hushed for a deeply poignant memorial before the fight as 10 bells rang in remembrance of Manchester's own Ricky Hatton, who succumbed at age 46 in September.
It was the premier televised fight night in the urban center since Hatton's passing. As the final chime ended, the stillness transitioned to a roar of "there's just one Ricky Hatton".
The competition inside the ropes matched the sentiment. Arthur was knocked down by a powerful punch squarely on the face in the initial stage, getting up unsteadily to his position on the referee's count.
But the traditional red attire of Arthur soon came forward again. Across the ring, Rea - in rival City blue - was injured soon, significant bruising developing under his eye as the duo landed punishing blows.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action seldom decreased over the full distance.
Arthur barely secured the verdict with official scores of draw, narrow lead and wider gap, but both fighters were relentless and full of heart, all the qualities their inspiration the legend embodied.
