UK light heavyweight Buatsi earned a win yet disappointing debut to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a competitive ten-round contest at the boxing arena.
But the challenger had his moments, delivering effective individual punches in a contest where the techniques never quite clicked, with constant grabbing disrupting the action.
Two judges judged it 96-94 for to the winner, with the third a even score.
"It wasn't my best showing but what do champions do? They win," the victor said in the ringside as he was met by disapproval from the crowd.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Some ringside observers believed the challenger, 31, merited the victory but the contender suffered the second setback of his 28-match career.
Buatsi Earns Triumph in Slow Affair
The fighter's advancement has slowed in recent years through promotional disputes and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now stands trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under recent support.
He began cautiously, with the two boxers willing to overcommit in a tentative initial rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after breaking his hand mid-fight, was competing in only his second fight at light heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for the favorite, who worked behind a protective stance to edge the cleaner stanzas.
The crowd's patience wore thin because of frequent holding, with the challenger going down various instances during grappling.
The underdog ended stronger, but many rounds were challenging to assess. Nevertheless, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Tribute Inspires Local Rivalry Contest
In the secondary fight, Arthur overcame Rea by split-decision in a outstanding all-Manchester contest to secure the European light heavyweight championship.
The stadium became quiet for a extremely emotional memorial before the fight as 10 bells tolled in remembrance of Manchester's own Ricky Hatton, who succumbed at age 46 in last month.
It was the initial significant broadcast fight night in the location since Hatton's death. As the concluding sound ended, the stillness became a shout of "only one Ricky Hatton".
The fighting within the ring reflected the emotion. The eventual winner was floored by a powerful punch directly to the chin in the second round, getting up unsteadily to his position on the eight count.
But the traditional red attire of Arthur soon pressed ahead again. Across the ring, the opponent - in competitive blue - was damaged soon, significant bruising developing under his orbital area as the fighters landed hard punches.
The challenger, twenty-seven, landed power punches but the champion, 34, responded in kind with powerful upward punches as the pace seldom decreased over twelve rounds.
The victor barely secured the result with scoring tallies of draw, narrow lead and wider gap, but both fighters were persistent and brave, exactly what their inspiration Hatton embodied.
