British light-heavyweight Buatsi earned a win yet disappointing beginning to life under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a close ten-round contest at the Manchester venue.
But Parker found success, landing some telling individual punches in a fight where the styles failed to mesh, with frequent clinching disrupting the contest.
The scoring judges judged it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest display but how do champions respond? They prevail," the victor commented in the ringside as he was faced disapproval from the spectators.
The Londoner got back to winning after his first professional defeat - an epic battle with Callum Smith in February - to secure a 20th career victory.
Some ringside observers felt the challenger, thirty-one, should have been awarded the decision but the Derbyshire fighter suffered the second loss of his 28-fight professional journey.
Buatsi Secures Win in Uneventful Affair
Buatsi's progress has plateaued in recent years through management issues and considerable time of lack of fights.
Once tipped as the rising talent of British boxing, he now is positioned trying to achieve expectations - maybe in what appears to be a last chance - under fresh management.
He started carefully, with neither fighter ready to overcommit in a cagey early stages.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after suffering a hand injury mid-fight, was participating in his second fight at light heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a tight guard to edge the better stanzas.
The audience's tolerance decreased because of regular grabbing, with Parker slipping to the canvas multiple occasions during clinches.
The underdog closed well, but multiple periods were challenging to assess. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just one round.
The victor advances, but with the presence of hard hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Hatton Tribute Fuels Local Rivalry Fight
In the supporting bout, Arthur overcame Bradley Rea by split-decision in a outstanding local rivalry contest to win the European light-heavyweight championship.
The stadium grew hushed for a deeply poignant memorial prior to the bout as ten bells sounded in memory of Manchester's own Hatton, who succumbed 46 years old in recently.
It was the premier televised fight night in the city since the passing of Hatton. As the final chime ended, the stillness became a chant of "only one Hatton".
The competition during the bout matched the sentiment. The eventual winner was floored by a significant blow squarely on the chin in the second round, standing uncertainly to his footing on the referee's count.
But the traditional red shorts of Arthur soon came forward again. On the opposite side, the opponent - in rival City blue - was damaged early, significant bruising forming under his orbital area as the fighters exchanged punishing blows.
The challenger, 27, landed power punches but Arthur, 34, fought fire with fire with stinging uppercuts as the intensity hardly diminished over the full distance.
The victor edged the decision with scoring tallies of even score, close margin and wider gap, but each competitor were relentless and courageous, exactly what their hero the legend embodied.
