British light heavyweight Buatsi secured a victory yet unimpressive start to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a tight 10-round fight at the Manchester venue.
But Parker found success, landing some telling clean blows in a contest where the styles never quite clicked, with excessive holding marring the contest.
The officials scored it 96-94 to the winner, with the final judge a even score.
"It wasn't my greatest showing but how do champions respond? They prevail," Buatsi said in the arena as he was met by disapproval from the audience.
The British fighter got back to winning after his initial pro loss - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Several boxing experts thought Parker, thirty-one, should have been awarded the decision but the British boxer endured the second loss of his 28-bout professional journey.
Buatsi Claims Win in Uneventful Encounter
Buatsi's progress has stalled in recent times through promotional disputes and considerable time of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now stands trying to achieve expectations - maybe in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors prepared to overcommit in a tentative early stages.
The challenger, 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 fight at light heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for the favorite, who worked behind a tight guard to edge the better periods.
The crowd's patience diminished because of constant clinching, with the challenger going down multiple occasions during close exchanges.
Parker finished the stronger, but many rounds were hard to judge. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, giving Buatsi just a single round.
The victor moves on, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Tribute Inspires Manchester Derby Contest
In the co-main event, Arthur overcame Rea by split-decision in a outstanding Manchester vs Manchester contest to secure the European light-heavyweight title.
The arena grew hushed for a profoundly moving tribute prior to the bout as 10 bells sounded in remembrance of Manchester's own Ricky Hatton, who died at age 46 in recently.
It was the premier televised fight night in the city since the passing of Hatton. As the final chime disappeared, the quiet gave way to a chant of "there's only one Hatton".
The competition inside the ropes matched the feeling. The eventual winner was floored by a significant blow directly to the chin in the second round, getting up unsteadily to his feet on the eight count.
But the traditional red shorts of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was damaged quickly, significant bruising appearing under his orbital area as the fighters landed hard punches.
The challenger, 27, landed power punches but the champion, 34, responded in kind with effective uppercuts as the action seldom decreased over the full distance.
Arthur narrowly won the result with scoring tallies of draw, 115-113 and clearer margin, but the two athletes were determined and courageous, all the qualities their idol Hatton stood for.
