British light heavyweight Buatsi made a winning yet unimpressive debut to his career under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a split decision in a competitive 10-round fight at the Manchester venue.
But the challenger had his moments, landing some telling individual punches in a fight where the techniques never quite clicked, with constant grabbing marring the contest.
The scoring judges had it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my best showing but what defines champions? They prevail," Buatsi stated in the ring as he was faced boos from the crowd.
The Londoner bounced back after his first professional defeat - an memorable fight with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers felt the challenger, 31, should have been awarded the victory but the British boxer suffered the second defeat of his 28-bout professional journey.
The Champion Earns Victory in Uneventful Encounter
The fighter's advancement has plateaued in recent years through management issues and long spells of lack of fights.
Earlier forecast as the next star of UK boxing, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a last chance - under recent support.
He began cautiously, with both competitors prepared to take risks in a cagey initial rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after damaging his hand during the bout, was making just his second fight at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, making life awkward for the favorite, who operated with a protective stance to barely take the cleaner stanzas.
The spectators' acceptance decreased because of constant clinching, with the challenger slipping to the canvas multiple occasions during clinches.
Parker finished the stronger, but multiple periods were difficult to score. Nevertheless, former world champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
The victor progresses, but with the caliber of heavy hitter Benavidez, and Russian champion Bivol leading the category, the path to championship success - judging by this showing - still appears challenging.
Hatton Memorial Motivates All-Manchester Battle
In the co-main event, Arthur overcame Rea by divided decision in a excellent all-Manchester fight to secure the continental championship.
The arena became quiet for a extremely emotional tribute before the fight as ten bells rang in remembrance of the city's native Ricky Hatton, who passed away aged 46 in recently.
It was the premier televised match card in the city since Hatton's passing. As the final chime disappeared, the quiet became a chant of "there's only one Ricky Hatton".
The competition during the bout reflected the feeling. The eventual winner was floored by a powerful punch flush on the chin in the second round, rising shakily to his position on the count of eight.
But the traditional red attire of Arthur soon advanced again. Across the ring, Rea - in rival City blue - was injured early, heavy swelling appearing under his face as the pair exchanged punishing blows.
Rea, twenty-seven, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the pace hardly diminished over the full distance.
The victor barely secured the result with judges scorecards of 114-114, close margin and wider gap, but each competitor were relentless and full of heart, exactly what their inspiration the legend embodied.
