UK light heavyweight Buatsi made a winning yet unimpressive debut to life under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a competitive ten-round contest at the Co-op Live Arena.
But Parker landed significant shots, delivering effective individual punches in a contest where the approaches never quite clicked, with frequent clinching spoiling the fight.
The scoring judges had it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest display but what do champions do? They succeed," the victor commented in the arena as he was met by negative reactions from the spectators.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts felt the challenger, 31, should have been awarded the win but the Derbyshire fighter suffered the second loss of his 28-bout professional journey.
Buatsi Claims Win in Slow Encounter
The fighter's advancement has slowed in recent years through management issues and long spells of inactivity.
Earlier forecast as the next star of British boxing, he now finds himself trying to fulfil that early promise - maybe in what appears to be a last chance - under fresh management.
He began cautiously, with the two boxers ready to overcommit in a cagey opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after damaging his hand in the contest, was competing in only his second bout at the higher weight class.
By the fight's midpoint, Parker had kept it close, creating difficulties for the favorite, who utilized a protective stance to barely take the more effective periods.
The spectators' acceptance diminished because of regular grabbing, with the challenger slipping to the canvas several times during clinches.
Parker closed well, but many rounds were hard to judge. However, ex-champion the boxing analyst - working with Dazn - had it particularly wide for Parker, awarding Buatsi just one round.
Buatsi moves on, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still appears challenging.
Hatton Tribute Motivates Local Rivalry Battle
In the supporting bout, Lyndon Arthur beat Rea by divided decision in a excellent local rivalry battle to win the European light heavyweight championship.
The venue became quiet for a extremely emotional homage prior to the bout as ten bells sounded in honor of Manchester's own Hatton, who succumbed 46 years old in last month.
It was the first major televised fight night in the urban center since Hatton's passing. As the last bell ended, the quiet became a roar of "there's just one Ricky Hatton".
The fighting inside the ropes equaled the emotion. Arthur was floored by a left hook squarely on the chin in the initial stage, standing uncertainly to his position on the referee's count.
But the Manchester United-red attire of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was injured quickly, significant bruising appearing under his face as the fighters landed punishing blows.
The challenger, 27, connected with strong blows but the champion, 34, fought fire with fire with stinging uppercuts as the intensity hardly diminished over twelve rounds.
Arthur narrowly won the result with official scores of draw, narrow lead and 115-112, but each competitor were determined and full of heart, all the qualities their inspiration the legend represented.
