British light-heavyweight Buatsi secured a victory yet underwhelming beginning to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a close ten-round fight at the Manchester venue.
But Parker found success, connecting with powerful clean blows in a match where the styles failed to mesh, with frequent clinching disrupting the contest.
The officials had it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my best performance but what do champions do? They prevail," Buatsi said in the arena as he was met by boos from the crowd.
The British fighter bounced back after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Various analysts believed Parker, thirty-one, merited the win but the Derbyshire fighter suffered the second loss of his 28-match career.
Buatsi Earns Victory in Slow Match
His career development has stalled in the past few years through management issues and extended periods of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now stands trying to achieve expectations - possibly in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with the two boxers ready to be aggressive in a cagey opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second appearance at light-heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for Buatsi, who operated with a tight guard to narrowly win the cleaner rounds.
The spectators' acceptance diminished because of constant clinching, with Parker falling to the floor various instances during grappling.
Parker finished the stronger, but several stanzas were hard to judge. However, former world champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Russian star Bivol leading the category, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Tribute Fuels Manchester Derby Fight
In the supporting bout, Arthur defeated Rea by split-decision in a excellent local rivalry contest to secure the European light-heavyweight title.
The venue grew hushed for a extremely emotional memorial prior to the bout as a bell ceremony sounded in remembrance of the city's native Hatton, who succumbed at age 46 in September.
It was the first major televised fight night in the location since the passing of Hatton. As the concluding sound ended, the quiet transitioned to a chant of "there's just one Ricky Hatton".
The action within the ring equaled the feeling. The eventual winner was knocked down by a significant blow flush on the jaw in the initial stage, getting up unsteadily to his position on the eight count.
But the traditional red shorts of the fighter soon pressed ahead again. From the other corner, Rea - in opposing blue - was damaged early, noticeable damage appearing under his eye as the pair landed hard punches.
Rea, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with effective uppercuts as the pace hardly diminished over the full distance.
The victor barely secured the result with official scores of 114-114, narrow lead and 115-112, but both fighters were persistent and courageous, exactly what their inspiration the legend stood for.
