British light heavyweight Buatsi earned a win yet disappointing start to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a tight ten-round bout at the Co-op Live Arena.
But Parker had his moments, landing some telling single shots in a match where the styles didn't complement each other, with frequent clinching disrupting the action.
The scoring judges judged it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my finest display but what do champions do? They prevail," the victor stated in the arena as he was faced boos from the crowd.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in last winter - to claim a 20th pro success.
Several boxing experts thought the challenger, thirty-one, merited the decision but the Derbyshire fighter experienced the second defeat of his 28-bout career.
The Champion Secures Victory in Slow Affair
The fighter's advancement has plateaued in recent times through contract problems and long spells of lack of fights.
Earlier forecast as the future of the British fight scene, he now finds himself trying to realize his potential - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors willing 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 suffering a hand injury mid-fight, was competing in only his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who utilized a protective stance to barely take the better rounds.
The crowd's patience wore thin amid regular grabbing, with the challenger slipping to the canvas multiple occasions during grappling.
The underdog finished the stronger, but multiple periods were difficult to score. Nevertheless, ex-champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
The victor moves on, but with the likes of heavy hitter David Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Tribute Inspires All-Manchester Fight
In the co-main event, Arthur beat Bradley Rea by divided decision in a terrific all-Manchester battle to win the European light heavyweight championship.
The venue fell silent for a profoundly moving tribute before the fight as ten bells rang in memory of local hero Hatton, who passed away at age 46 in recently.
It was the premier televised boxing event in the urban center since Hatton's passing. As the concluding sound ended, the stillness became a shout of "only one Hatton".
The fighting during the bout matched the emotion. Arthur was floored by a powerful punch squarely on the chin in the second round, rising shakily to his footing on the count of eight.
But the Manchester United-red equipment of the fighter soon advanced again. On the opposite side, the opponent - in opposing blue - was injured early, noticeable damage appearing under his face as the fighters landed hard punches.
The challenger, 27, landed power punches but the champion, thirty-four, fought fire with fire with stinging uppercuts as the intensity seldom decreased over twelve rounds.
The victor barely secured the verdict with scoring tallies of even score, narrow lead and 115-112, but both fighters were relentless and brave, exactly what their idol the legend stood for.
