British light-heavyweight Buatsi made a winning yet unimpressive beginning to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a majority decision in a close 10-round contest at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful individual punches in a contest where the approaches never quite clicked, with excessive holding marring the fight.
The scoring judges judged it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my greatest performance but what defines champions? They prevail," Buatsi commented in the ringside as he was met by disapproval from the crowd.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a 20th career victory.
Various analysts felt the challenger, 31, should have been awarded the win but the contender endured the second loss of his 28-fight career.
Buatsi Earns Victory in Slow Match
His career development has slowed in recent years through promotional disputes and long spells of inactivity.
Once tipped as the rising talent of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors ready to be aggressive in a cagey early stages.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was making just his second fight at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for Buatsi, who operated with a tight guard to narrowly win the more effective stanzas.
The crowd's patience diminished during frequent holding, with Parker going down several times during clinches.
The underdog closed well, but several stanzas were hard to judge. Nevertheless, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, giving Buatsi just a single round.
Buatsi advances, but with the presence of power puncher Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - based on this performance - still seems difficult.
Hatton Tribute Fuels All-Manchester Contest
In the supporting bout, Arthur overcame Rea by divided decision in a terrific Manchester vs Manchester fight to secure the European light heavyweight belt.
The stadium fell silent for a profoundly moving memorial prior to the bout as ten bells tolled in remembrance of local hero Ricky Hatton, who died 46 years old in recently.
It was the premier televised fight night in the city since the passing of Hatton. As the last bell ended, the stillness became a chant of "there's only one Ricky Hatton".
The action within the ring matched the emotion. The eventual winner was floored by a left hook directly to the chin in the initial stage, getting up unsteadily to his position on the referee's count.
But the traditional red shorts of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was marked up quickly, significant bruising appearing under his orbital area as the fighters landed powerful shots.
The challenger, twenty-seven, connected with strong blows but the champion, 34, fought fire with fire with effective uppercuts as the action rarely dropped over the full distance.
Arthur narrowly won the decision with scoring tallies of 114-114, close margin and 115-112, but the two athletes were determined and full of heart, all the qualities their hero the legend stood for.
