UK light-heavyweight Buatsi secured a victory yet disappointing debut to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a judges' verdict in a close 10-round fight at the boxing arena.
But the challenger landed significant shots, landing some telling individual punches in a match where the techniques failed to mesh, with constant grabbing disrupting the action.
The scoring judges had it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my finest showing but how do champions respond? They win," Buatsi commented in the ring as he was greeted with 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 20th career victory.
Various analysts felt Parker, 31, deserved the win but the British boxer endured the second loss of his 28-fight career.
Buatsi Secures Victory in Slow Encounter
Buatsi's progress has plateaued in recent years through management issues and considerable time of lack of fights.
Earlier forecast as the future of UK boxing, he now is positioned trying to fulfil that early promise - perhaps in what feels like a last chance - under new promotional backing.
He started carefully, with neither fighter prepared to overcommit in a calculated early stages.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second bout at light heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for Buatsi, who utilized a protective stance to barely take the cleaner stanzas.
The spectators' acceptance diminished amid constant clinching, with the challenger slipping to the canvas multiple occasions during close exchanges.
Parker finished the stronger, but several stanzas were hard to judge. Although, previous titleholder the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, giving Buatsi just only one stanza.
Buatsi moves on, but with the presence of power puncher David Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - based on this performance - still appears challenging.
Hatton Homage Inspires Manchester Derby Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding Manchester vs Manchester contest to capture the European light-heavyweight title.
The stadium grew hushed for a deeply poignant memorial prior to the bout as ten bells sounded in honor of Manchester's own Ricky Hatton, who died 46 years old in September.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the last bell faded, the stillness became a roar of "only one Ricky Hatton".
The action inside the ropes matched the emotion. Arthur was floored by a left hook directly to the chin in the second round, standing uncertainly to his footing on the referee's count.
But the red-colored attire of the fighter soon pressed ahead again. Across the ring, the opponent - in competitive blue - was damaged early, noticeable damage developing under his face as the duo exchanged powerful shots.
Rea, 27, delivered effective strikes but the champion, 34, matched the intensity with effective uppercuts as the pace hardly diminished over 12 rounds.
The victor narrowly won the verdict with scoring tallies of even score, narrow lead and wider gap, but each competitor were relentless and courageous, all the qualities their idol Hatton stood for.
