UK light-heavyweight Buatsi earned a win yet disappointing debut to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a split decision in a competitive ten-round contest at the Manchester venue.
But the challenger had his moments, delivering effective individual punches in a match where the styles never quite clicked, with excessive holding disrupting the fight.
Two judges scored it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest showing but how do champions respond? They succeed," the victor stated in the ringside as he was greeted with boos from the audience.
The Londoner got back to winning after his first professional defeat - an thrilling contest with Callum Smith in last winter - to earn a 20th career victory.
Some ringside observers thought the challenger, 31, should have been awarded the victory but the Derbyshire fighter suffered the second defeat of his 28-fight professional journey.
The Champion Claims Victory in Uneventful Encounter
His career development has slowed in recent times through management issues and long spells of inactivity.
Once tipped as the future of British boxing, he now finds himself trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under recent support.
He started carefully, with neither fighter willing to be aggressive in a cagey initial rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after breaking his hand mid-fight, was making just his second appearance at light-heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for the favorite, who worked behind a tight guard to narrowly win the cleaner periods.
The audience's tolerance decreased during constant clinching, with the challenger falling to the floor several times during clinches.
The underdog closed well, but several stanzas were hard to judge. Although, former world champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, giving Buatsi just a single round.
Buatsi progresses, but with the likes of heavy hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the road to world glory - judging by this showing - still looks steep.
Hatton Homage Fuels Manchester Derby Battle
In the co-main event, Arthur beat Rea by close verdict in a outstanding Manchester vs Manchester fight to capture the European light-heavyweight title.
The venue grew hushed for a deeply poignant tribute before the fight as 10 bells sounded in memory of Manchester's own Hatton, who died at age 46 in recently.
It was the initial significant broadcast match card in the location since Hatton's death. As the final chime faded, the quiet became a roar of "there's only one Hatton".
The action inside the ropes equaled the sentiment. Arthur was floored by a left hook squarely on the face in the early round, rising shakily to his footing on the count of eight.
But the Manchester United-red equipment of the fighter soon advanced again. Across the ring, the opponent - in rival City blue - was damaged early, heavy swelling forming under his eye as the fighters exchanged powerful shots.
The challenger, twenty-seven, landed power punches but Arthur, 34, responded in kind with stinging uppercuts as the intensity hardly diminished over 12 rounds.
Arthur barely secured the decision with judges scorecards of even score, narrow lead and wider gap, but the two athletes were persistent and courageous, everything their idol the legend represented.
