British light heavyweight Buatsi secured a victory yet disappointing start to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a majority decision in a competitive ten-round contest at the boxing arena.
But the challenger found success, landing some telling single shots in a match where the techniques didn't complement each other, with frequent clinching marring the contest.
Two judges judged it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best performance but what defines champions? They prevail," Buatsi stated in the arena as he was greeted with disapproval from the crowd.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to secure a 20th pro success.
Various analysts felt the challenger, 31, deserved the decision but the Derbyshire fighter experienced the second defeat of his 28-match professional journey.
The Champion Secures Victory in Uneventful Match
Buatsi's progress has stalled in the past few years through promotional disputes and considerable time of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to realize his potential - perhaps in what appears to be a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors willing to be aggressive in a tentative initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after damaging his hand during the bout, was making just his second bout at light heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for the favorite, who utilized a protective stance to edge the better stanzas.
The crowd's patience decreased amid frequent holding, with Parker going down multiple occasions during close exchanges.
The underdog finished the stronger, but many rounds were challenging to assess. However, former world champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
Buatsi advances, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - based on this performance - still looks steep.
Hatton Homage Motivates All-Manchester Contest
In the secondary fight, Lyndon Arthur defeated Rea by split-decision in a outstanding all-Manchester battle to capture the continental title.
The arena became quiet for a deeply poignant memorial ahead of the contest as 10 bells tolled in remembrance of local hero Ricky Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the final chime faded, the silence gave way to a chant of "there's only one Ricky Hatton".
The competition within the ring reflected the sentiment. The eventual winner was knocked down by a powerful punch flush on the face in the early round, getting up unsteadily to his footing on the eight count.
But the red-colored attire of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was injured early, heavy swelling developing under his face as the duo landed punishing blows.
Rea, 27, landed power punches but the champion, 34, matched the intensity with stinging uppercuts as the intensity seldom decreased over twelve rounds.
The victor narrowly won the decision with official scores of 114-114, close margin and wider gap, but each competitor were relentless and courageous, exactly what their hero the legend embodied.
