British light-heavyweight Buatsi secured a victory yet disappointing beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a close 10-round bout at the boxing arena.
But Parker had his moments, delivering effective single shots in a match where the techniques failed to mesh, with constant grabbing disrupting the action.
Two judges judged it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my greatest performance but what defines champions? They prevail," the victor stated in the ringside as he was faced negative reactions from the audience.
The Londoner got back to winning after his initial pro loss - an epic battle with Callum Smith in February - to earn a 20th career victory.
Several boxing experts believed the challenger, 31, deserved the win but the contender experienced the second loss of his 28-fight career.
The Champion Secures Win in Slow Affair
Buatsi's progress has stalled in recent times through contract problems and long spells of inactivity.
Once tipped as the rising talent of UK boxing, he now finds himself trying to achieve expectations - perhaps in what appears to be a ultimate opportunity - under recent support.
He started carefully, with the two boxers prepared to take risks in a cagey opening few rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was competing in only his second bout at the higher weight class.
By the fight's midpoint, the underdog had kept it close, making life awkward for the favorite, who worked behind a protective stance to edge the better periods.
The audience's tolerance decreased amid constant clinching, with the challenger falling to the floor multiple occasions during close exchanges.
The underdog closed well, but several stanzas were difficult to score. Although, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
The victor advances, but with the likes of hard hitter David Benavidez, and Russian champion Bivol leading the category, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Tribute Inspires Local Rivalry Fight
In the co-main event, Arthur overcame Bradley Rea by close verdict in a excellent local rivalry battle to capture the European light-heavyweight belt.
The venue became quiet for a extremely emotional homage ahead of the contest as a bell ceremony tolled in memory of Manchester's own Ricky Hatton, who succumbed at age 46 in last month.
It was the premier televised boxing event in the location since Hatton's passing. As the final chime disappeared, the stillness gave way to a shout of "there's only one Ricky Hatton".
The competition within the ring reflected the sentiment. Arthur was floored by a significant blow flush on the face in the initial stage, standing uncertainly to his position on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. From the other corner, Rea - in competitive blue - was marked up soon, heavy swelling forming under his face as the fighters landed powerful shots.
Rea, twenty-seven, landed power punches but the champion, 34, fought fire with fire with stinging uppercuts as the intensity seldom decreased over twelve rounds.
The victor edged the result with judges scorecards of 114-114, close margin and clearer margin, but the two athletes were persistent and courageous, exactly what their inspiration Hatton embodied.
