UK light-heavyweight Buatsi earned a win yet underwhelming start 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 majority decision in a close ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful individual punches in a match where the techniques didn't complement each other, with frequent clinching spoiling the contest.
The officials judged it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest performance but how do champions respond? They win," the victor commented in the ringside as he was met by disapproval from the audience.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in February - to claim a twentieth professional win.
Various analysts believed the challenger, 31, merited the win but the contender endured the second loss of his 28-bout professional journey.
Buatsi Claims Triumph in Dull Match
The fighter's advancement has stalled in the past few years through promotional disputes and long spells of inactivity.
Earlier forecast 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 fresh management.
He began cautiously, with neither fighter ready to take risks in a tentative 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 mid-fight, was making just his second bout at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for Buatsi, who operated with a solid defense to narrowly win the cleaner stanzas.
The crowd's patience decreased during frequent holding, with Parker slipping to the canvas several times during close exchanges.
Parker closed well, but multiple periods were hard to judge. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the presence of hard hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - based on this performance - still appears challenging.
Hatton Homage Motivates Manchester Derby Fight
In the secondary fight, Arthur beat Rea by divided decision in a outstanding all-Manchester contest to capture the continental title.
The stadium grew hushed for a extremely emotional memorial ahead of the contest as ten bells sounded in remembrance of local hero Ricky Hatton, who passed away aged 46 in last month.
It was the first major televised boxing event in the urban center since the passing of Hatton. As the final chime disappeared, the stillness gave way to a shout of "there's just one Ricky Hatton".
The fighting inside the ropes matched the emotion. Arthur was floored by a left hook flush on the chin in the initial stage, standing uncertainly to his feet on the eight count.
But the traditional red equipment of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was marked up early, significant bruising forming under his orbital area as the fighters traded punishing blows.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the action seldom decreased over the full distance.
Arthur edged the result with scoring tallies of draw, 115-113 and clearer margin, but each competitor were persistent and full of heart, exactly what their hero the legend represented.
