UK light-heavyweight Buatsi secured a victory yet underwhelming beginning to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a majority decision in a tight ten-round contest at the Manchester venue.
But Parker found success, connecting with powerful individual punches in a contest where the styles didn't complement each other, with frequent clinching marring the action.
The scoring judges had it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my finest performance but what defines champions? They win," the victor stated in the ringside as he was greeted with boos from the audience.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in February - to secure a 20th career victory.
Various analysts believed the challenger, thirty-one, should have been awarded the decision but the contender endured the second defeat of his 28-bout career.
The Champion Secures Triumph in Uneventful Encounter
His career development has slowed in recent times through promotional disputes and extended periods of lack of fights.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to realize his potential - maybe in what seems like a final roll of the dice - under fresh management.
He started carefully, with both competitors prepared to take risks in a tentative initial rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was participating in his second fight at light heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for Buatsi, who worked behind a solid defense to edge the better rounds.
The spectators' acceptance diminished because of constant clinching, with Parker falling to the floor various instances during grappling.
The underdog finished the stronger, but many rounds were challenging to assess. However, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, scoring for Buatsi just a single round.
The victor advances, but with the caliber of hard hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still seems difficult.
Hatton Tribute Inspires Manchester Derby Fight
In the co-main event, Arthur defeated Rea by split-decision in a outstanding all-Manchester battle to capture the European light-heavyweight title.
The arena fell silent for a deeply poignant homage ahead of the contest as ten bells sounded in remembrance of local hero Hatton, who succumbed 46 years old in last month.
It was the premier televised fight night in the urban center since Hatton's death. As the last bell disappeared, the stillness transitioned to a shout of "only one Ricky Hatton".
The fighting within the ring equaled the feeling. Arthur was sent to the canvas by a left hook directly to the chin in the initial stage, getting up unsteadily to his footing on the referee's count.
But the traditional red shorts of the fighter soon pressed ahead again. Across the ring, Rea - in rival City blue - was injured soon, noticeable damage forming under his orbital area as the fighters landed punishing blows.
Rea, 27, delivered effective strikes but the champion, 34, responded in kind with effective uppercuts as the action rarely dropped over 12 rounds.
Arthur edged the decision with judges scorecards of draw, 115-113 and clearer margin, but each competitor were relentless and brave, everything their idol the legend embodied.
