British light heavyweight Buatsi secured a victory yet disappointing beginning to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a competitive 10-round contest at the Manchester venue.
But Parker had his moments, landing some telling clean blows in a contest where the approaches didn't complement each other, with excessive holding disrupting the contest.
Two judges judged it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best display but what do champions do? They succeed," Buatsi commented in the arena as he was faced disapproval from the audience.
The Londoner bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to secure a 20th pro success.
Various analysts felt the challenger, thirty-one, merited the victory but the contender endured the second defeat of his 28-fight career.
Buatsi Secures Win in Dull Match
His career development has slowed in recent times through contract problems and extended periods of inactivity.
Once tipped as the next star of the British fight scene, he now is positioned trying to realize his potential - perhaps in what seems like a last chance - under new promotional backing.
He started carefully, with neither fighter prepared to take risks in a cagey early stages.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in 2022 after suffering a hand injury in the contest, was competing in only his second fight at light-heavyweight.
By the middle rounds, Parker had kept it close, causing problems for Buatsi, who utilized a tight guard to barely take the cleaner periods.
The crowd's patience diminished because of regular grabbing, with the challenger going down multiple occasions during grappling.
The underdog closed well, but several stanzas were difficult to score. However, former world champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the presence of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Hatton Tribute Motivates All-Manchester Battle
In the co-main event, Lyndon Arthur overcame Rea by split-decision in a terrific all-Manchester battle to secure the European light heavyweight championship.
The stadium fell silent for a profoundly moving memorial prior to the bout as ten bells sounded in memory of the city's native Ricky Hatton, who died 46 years old in recently.
It was the premier televised fight night in the urban center since Hatton's passing. As the last bell ended, the stillness transitioned to a shout of "only one Hatton".
The fighting during the bout matched the emotion. Arthur was floored by a significant blow squarely on the face in the early round, rising shakily to his position on the count of eight.
But the red-colored shorts of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was marked up soon, heavy swelling appearing under his face as the duo traded powerful shots.
Rea, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with stinging uppercuts as the action hardly diminished over 12 rounds.
Arthur narrowly won the verdict with official scores of even score, narrow lead and 115-112, but each competitor were determined and courageous, everything their hero the legend represented.
