British light-heavyweight Buatsi earned a win yet disappointing beginning to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a competitive ten-round bout at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective individual punches in a fight where the styles never quite clicked, with constant grabbing disrupting the action.
The officials scored it 96-94 to Buatsi, with the third a even score.
"It wasn't my finest display but what do champions do? They succeed," the victor said in the ringside as he was greeted with disapproval from the crowd.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in February - to claim a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, deserved the win but the contender suffered the second loss of his 28-match professional journey.
Buatsi Earns Triumph in Dull Encounter
His career development has plateaued in recent years through management issues and extended periods of lack of fights.
Previously predicted as the next star of the British fight scene, he now is positioned trying to realize his potential - possibly in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter prepared to be aggressive in a cagey early stages.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second appearance at light heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for Buatsi, who utilized a tight guard to barely take the better stanzas.
The spectators' acceptance diminished amid regular grabbing, with the challenger falling to the floor various instances during grappling.
Parker ended stronger, but multiple periods were challenging to assess. Although, previous titleholder Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, giving Buatsi just only one stanza.
Buatsi advances, but with the likes of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Hatton Homage Motivates Local Rivalry Fight
In the co-main event, Arthur overcame Rea by close verdict in a outstanding local rivalry battle to capture the European light-heavyweight belt.
The stadium grew hushed for a profoundly moving tribute prior to the bout as 10 bells sounded in remembrance of the city's native Hatton, who succumbed aged 46 in September.
It was the premier televised boxing event in the location since Hatton's death. As the concluding sound disappeared, the stillness became a shout of "there's only one Hatton".
The fighting during the bout reflected the sentiment. Arthur was knocked down by a left hook squarely on the jaw in the early round, standing uncertainly to his feet on the count of eight.
But the Manchester United-red shorts of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was injured early, significant bruising forming under his orbital area as the pair exchanged powerful shots.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the pace seldom decreased over the full distance.
The victor edged the verdict with scoring tallies of even score, close margin and wider gap, but each competitor were relentless and full of heart, everything their hero Hatton embodied.
