British light-heavyweight Buatsi made a winning yet unimpressive start to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a majority decision in a competitive ten-round contest at the Co-op Live Arena.
But the challenger found success, connecting with powerful clean blows in a match where the techniques failed to mesh, with excessive holding spoiling the contest.
Two judges scored it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest showing but what do champions do? They prevail," the victor said in the ringside as he was met by disapproval from the audience.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in February - to secure a 20th career victory.
Various analysts thought the challenger, 31, should have been awarded the victory but the British boxer endured the second defeat of his 28-fight career.
The Champion Earns Victory in Slow Match
His career development has plateaued in recent times through promotional disputes and long spells of lack of fights.
Earlier forecast as the next star of the British fight scene, he now is positioned trying to achieve expectations - possibly in what seems like a last chance - under recent support.
He began cautiously, with both competitors prepared to take risks in a cagey opening few rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after damaging his hand mid-fight, was competing in only his second bout at the higher weight class.
By the middle rounds, the underdog had kept it close, creating difficulties for the favorite, who worked behind a protective stance to narrowly win the more effective stanzas.
The crowd's patience wore thin during frequent holding, with the challenger falling to the floor multiple occasions during close exchanges.
The underdog closed well, but many rounds were difficult to score. Although, ex-champion the boxing analyst - working with the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor progresses, but with the caliber of heavy hitter Benavidez, and Russian star Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Tribute Motivates Manchester Derby Fight
In the supporting bout, Arthur beat Rea by split-decision in a outstanding all-Manchester battle to win the European light heavyweight championship.
The arena became quiet for a extremely emotional homage prior to the bout as ten bells tolled in honor of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the initial significant broadcast match card in the location since Hatton's passing. As the last bell ended, the silence became a shout of "there's just one Hatton".
The fighting within the ring reflected the feeling. The eventual winner was knocked down by a significant blow directly to the jaw in the second round, getting up unsteadily to his position on the referee's count.
But the traditional red equipment of the fighter soon came forward again. On the opposite side, Rea - in opposing blue - was damaged quickly, heavy swelling forming under his orbital area as the pair landed hard punches.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the pace rarely dropped over the full distance.
The victor barely secured the decision with judges scorecards of 114-114, close margin and clearer margin, but both fighters were persistent and full of heart, exactly what their inspiration the legend represented.
