UK light heavyweight Buatsi earned a win yet disappointing debut to his career under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a split decision in a tight ten-round fight at the boxing arena.
But the challenger landed significant shots, landing some telling single shots in a fight where the styles failed to mesh, with frequent clinching spoiling the fight.
The officials scored it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my greatest showing but what do champions do? They succeed," Buatsi said in the arena as he was met by disapproval from the spectators.
The Londoner got back to winning after his maiden career setback - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Various analysts believed the challenger, thirty-one, deserved the win but the contender experienced the second setback of his 28-bout career.
Buatsi Secures Triumph in Dull Affair
Buatsi's progress has slowed in recent years through promotional disputes and long spells of lack of fights.
Earlier forecast as the future of UK boxing, he now stands trying to realize his potential - possibly in what feels like a last chance - under new promotional backing.
He opened tentatively, with the two boxers ready to overcommit in a calculated initial rounds.
Parker, whose only previous defeat came at super middleweight against his former opponent in two years ago after damaging his hand mid-fight, was making just his second bout at light-heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who operated with a protective stance to edge the more effective rounds.
The audience's tolerance decreased amid constant clinching, with Parker falling to the floor various instances during clinches.
The underdog finished the stronger, but many rounds were hard to judge. However, former world champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for Parker, giving Buatsi just only one stanza.
The victor progresses, but with the presence of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Memorial Inspires All-Manchester Battle
In the co-main event, Lyndon Arthur defeated Bradley Rea by close verdict in a outstanding Manchester vs Manchester battle to win the European light-heavyweight belt.
The arena grew hushed for a extremely emotional tribute before the fight as a bell ceremony sounded in remembrance of the city's native Ricky Hatton, who succumbed 46 years old in September.
It was the first major televised fight night in the city since Hatton's passing. As the final chime ended, the stillness gave way to a roar of "there's only one Hatton".
The competition inside the ropes equaled the sentiment. Arthur was sent to the canvas by a powerful punch flush on the jaw in the early round, rising shakily to his feet on the count of eight.
But the red-colored attire of Arthur soon advanced again. On the opposite side, Rea - in opposing blue - was injured soon, noticeable damage appearing under his orbital area as the duo exchanged hard punches.
The challenger, 27, landed power punches but the champion, 34, fought fire with fire with powerful upward punches as the pace rarely dropped over the full distance.
The victor narrowly won the decision with judges scorecards of even score, narrow lead and 115-112, but both fighters were relentless and full of heart, everything their inspiration the legend embodied.
