British light heavyweight Buatsi earned a win yet disappointing beginning to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a split decision in a competitive ten-round bout at the Co-op Live Arena.
But Parker had his moments, delivering effective single shots in a match where the styles didn't complement each other, with frequent clinching spoiling the action.
Two judges had it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my finest display but what defines champions? They prevail," Buatsi said in the ringside as he was met by negative reactions from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with his previous opponent in last winter - to secure a 20th pro success.
Several boxing experts felt the challenger, 31, deserved the decision but the contender suffered the second loss of his 28-fight professional journey.
The Champion Earns Triumph in Slow Encounter
Buatsi's progress has slowed in recent years through contract problems and extended periods of inactivity.
Previously predicted as the future of UK boxing, he now is positioned trying to realize his potential - maybe in what appears to be a final roll of the dice - under fresh management.
He opened tentatively, with neither fighter willing to take risks in a cagey opening few rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was making just his second appearance at light-heavyweight.
By the middle rounds, Parker had kept it close, causing problems for Buatsi, who worked behind a tight guard to barely take the better stanzas.
The crowd's patience diminished during frequent holding, with the challenger slipping to the canvas various instances during grappling.
The underdog closed well, but many rounds were hard to judge. However, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, giving Buatsi just one round.
The victor advances, but with the presence of power puncher Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Motivates All-Manchester Fight
In the secondary fight, Lyndon Arthur defeated Bradley Rea by close verdict in a outstanding all-Manchester contest to capture the European light heavyweight title.
The stadium fell silent for a deeply poignant tribute before the fight as a bell ceremony sounded in memory of the city's native Hatton, who passed away at age 46 in recently.
It was the premier televised fight night in the city since Hatton's passing. As the concluding sound disappeared, the silence gave way to a roar of "there's just one Ricky Hatton".
The competition during the bout reflected the feeling. Arthur was floored by a significant blow directly to the face in the early round, getting up unsteadily to his feet on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. Across the ring, Rea - in competitive blue - was injured early, significant bruising appearing under his orbital area as the fighters exchanged powerful shots.
Rea, 27, landed power punches but the champion, thirty-four, matched the intensity with stinging uppercuts as the action seldom decreased over twelve rounds.
The victor edged the verdict with scoring tallies of 114-114, narrow lead and wider gap, but the two athletes were determined and full of heart, exactly what their idol the legend stood for.
