British light heavyweight Buatsi made a winning yet underwhelming debut to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a close 10-round fight at the boxing arena.
But Parker found success, landing some telling clean blows in a match where the approaches never quite clicked, with excessive holding disrupting the fight.
The officials scored it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my best performance but how do champions respond? They win," the victor commented in the ring as he was met by disapproval from the crowd.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in February - to claim a twentieth professional win.
Some ringside observers believed the challenger, thirty-one, merited the victory but the Derbyshire fighter endured the second loss of his 28-bout career.
Buatsi Claims Triumph in Dull Match
The fighter's advancement has slowed in recent times through management issues and considerable time of inactivity.
Once tipped as the next star of the British fight scene, he now stands trying to realize his potential - perhaps in what appears to be a last chance - under recent support.
He started carefully, with the two boxers prepared to be aggressive in a cagey initial rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was making just his second bout at the higher weight class.
By the fight's midpoint, Parker had made it competitive, causing problems for the favorite, who operated with a solid defense to edge the more effective periods.
The spectators' acceptance wore thin because of frequent holding, with the challenger slipping to the canvas various instances during close exchanges.
The underdog finished the stronger, but many rounds were hard to judge. Nevertheless, former world champion Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
The victor progresses, but with the likes of power puncher Benavidez, and Russian champion Bivol leading the category, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Tribute Fuels Manchester Derby Battle
In the supporting bout, Arthur beat Rea by split-decision in a terrific Manchester vs Manchester fight to win the European light heavyweight belt.
The arena fell silent for a deeply poignant memorial ahead of the contest as ten bells rang in honor of Manchester's own Hatton, who succumbed aged 46 in last month.
It was the first major televised boxing event in the urban center since Hatton's death. As the final chime faded, the stillness transitioned to a shout of "only one Ricky Hatton".
The action inside the ropes equaled the sentiment. Arthur was floored by a left hook flush on the chin in the initial stage, standing uncertainly to his feet on the count of eight.
But the traditional red equipment of the fighter soon pressed ahead again. From the other corner, the opponent - in rival City blue - was damaged early, noticeable damage developing under his eye as the duo traded hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with effective uppercuts as the pace seldom decreased over the full distance.
The victor edged the decision with judges scorecards of 114-114, narrow lead and clearer margin, but both fighters were determined and full of heart, exactly what their inspiration the legend represented.
