British light heavyweight Buatsi secured a victory yet disappointing debut to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a split decision in a close ten-round bout at the boxing arena.
But Parker had his moments, connecting with powerful individual punches in a contest where the styles never quite clicked, with frequent clinching disrupting the contest.
The officials had it 96-94 for to the winner, with the final judge a even score.
"It wasn't my greatest display but how do champions respond? They succeed," the victor commented in the ringside as he was met by disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in February - to claim a 20th career victory.
Some ringside observers thought the challenger, 31, merited the decision but the contender endured the second setback of his 28-bout career.
The Champion Claims Win in Slow Affair
The fighter's advancement has slowed in recent times through management issues and considerable time of lack of fights.
Once tipped as the next star of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with the two boxers ready to be aggressive in a tentative opening few rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was competing in only his second appearance at light-heavyweight.
By the fight's midpoint, Parker had kept it close, causing problems for Buatsi, who utilized a tight guard to narrowly win the cleaner periods.
The audience's tolerance decreased because of regular grabbing, with the challenger falling to the floor various instances during clinches.
The underdog closed well, but several stanzas were hard to judge. However, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, scoring for Buatsi just a single round.
Buatsi progresses, but with the likes of heavy hitter Benavidez, and Russian star Bivol leading the category, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Tribute Motivates Manchester Derby Fight
In the secondary fight, Arthur overcame Bradley Rea by close verdict in a outstanding Manchester vs Manchester fight to win the European light heavyweight championship.
The stadium grew hushed for a extremely emotional memorial before the fight as 10 bells sounded in memory of Manchester's own Hatton, who succumbed at age 46 in last month.
It was the premier televised match card in the location since the passing of Hatton. As the last bell disappeared, the stillness became a chant of "there's just one Hatton".
The competition within the ring equaled the emotion. Arthur was sent to the canvas by a powerful punch squarely on the jaw in the second round, getting up unsteadily to his footing on the referee's count.
But the traditional red equipment of the fighter soon advanced again. Across the ring, Rea - in competitive blue - was damaged quickly, significant bruising developing under his eye as the duo traded hard punches.
Rea, 27, landed power punches but the champion, 34, matched the intensity with stinging uppercuts as the action rarely dropped over 12 rounds.
The victor edged the verdict with scoring tallies of 114-114, close margin and 115-112, but each competitor were persistent and courageous, all the qualities their inspiration the legend represented.
