British light heavyweight Buatsi earned a win yet unimpressive debut to life under new promoters with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a close ten-round bout at the Manchester venue.
But the challenger had his moments, landing some telling individual punches in a fight where the styles failed to mesh, with constant grabbing marring the contest.
Two judges scored it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest showing but what defines champions? They succeed," the victor said in the ringside as he was met by disapproval from the crowd.
The Londoner got back to winning after his initial pro loss - an epic battle with his previous opponent in February - to claim a 20th pro success.
Some ringside observers believed Parker, 31, should have been awarded the win but the British boxer endured the second defeat of his 28-fight career.
The Champion Secures Victory in Dull Affair
The fighter's advancement has slowed in recent times through management issues and extended periods of lack of fights.
Previously predicted as the future of British boxing, he now stands trying to realize his potential - possibly in what appears to be a last chance - under fresh management.
He opened tentatively, with the two boxers willing to overcommit in a calculated early stages.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand in the contest, was competing in only his second bout at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, causing problems for Buatsi, who worked behind a tight guard to narrowly win the cleaner rounds.
The spectators' acceptance diminished amid frequent holding, with the challenger going down multiple occasions during clinches.
The underdog closed well, but several stanzas were challenging to assess. Nevertheless, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
Buatsi advances, but with the caliber of power puncher Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Hatton Homage Motivates All-Manchester Contest
In the co-main event, Arthur beat Bradley Rea by split-decision in a outstanding local rivalry contest to secure the European light heavyweight title.
The arena fell silent for a deeply poignant tribute ahead of the contest as 10 bells tolled in memory of the city's native Ricky Hatton, who died aged 46 in recently.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the concluding sound disappeared, the quiet became a roar of "only one Hatton".
The fighting within the ring matched the emotion. Arthur was floored by a significant blow flush on the face in the initial stage, standing uncertainly to his position on the referee's count.
But the Manchester United-red shorts of Arthur soon came forward again. Across the ring, Rea - in rival City blue - was marked up quickly, heavy swelling developing under his face as the pair landed punishing blows.
The challenger, 27, delivered effective strikes but the champion, 34, fought fire with fire with effective uppercuts as the intensity rarely dropped over the full distance.
Arthur narrowly won the result with scoring tallies of 114-114, narrow lead and 115-112, but each competitor were persistent and courageous, everything their hero Hatton stood for.
