UK light heavyweight Buatsi secured a victory yet disappointing start to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a majority decision in a close 10-round contest at the Co-op Live Arena.
But Parker found success, delivering effective clean blows in a contest where the approaches never quite clicked, with constant grabbing marring the action.
The officials had it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my finest performance but how do champions respond? They prevail," Buatsi stated in the ring as he was faced negative reactions from the spectators.
The Londoner got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, deserved the victory but the Derbyshire fighter experienced the second defeat of his 28-fight professional journey.
Buatsi Secures Victory in Slow Match
Buatsi's progress has plateaued in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the next star of British boxing, he now stands trying to realize his potential - possibly in what appears to be a final roll of the dice - under new promotional backing.
He began cautiously, with both competitors prepared to overcommit in a calculated initial rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was participating in his second appearance at light-heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for Buatsi, who operated with a tight guard to edge the cleaner rounds.
The audience's tolerance diminished during constant clinching, with the challenger falling to the floor multiple occasions during grappling.
Parker ended stronger, but multiple periods were hard to judge. Nevertheless, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the presence of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Homage Fuels Local Rivalry Fight
In the supporting bout, Lyndon Arthur overcame Bradley Rea by split-decision in a excellent local rivalry fight to win the European light heavyweight championship.
The venue became quiet for a extremely emotional homage ahead of the contest as 10 bells tolled in honor of the city's native Ricky Hatton, who succumbed 46 years old in recently.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the last bell ended, the stillness became a chant of "there's only one Ricky Hatton".
The fighting during the bout equaled the feeling. Arthur was floored by a left hook flush on the chin in the second round, getting up unsteadily to his position on the count of eight.
But the traditional red equipment of the fighter soon came forward again. On the opposite side, the opponent - in competitive blue - was injured early, significant bruising forming under his eye as the fighters landed punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with effective uppercuts as the pace rarely dropped over 12 rounds.
The victor narrowly won the result with judges scorecards of even score, narrow lead and wider gap, but each competitor were determined and courageous, everything their hero the legend represented.
