British light-heavyweight Buatsi earned a win yet disappointing debut to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a competitive ten-round fight at the Manchester venue.
But Parker found success, delivering effective single shots in a fight where the styles didn't complement each other, with frequent clinching disrupting the fight.
Two judges had it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my best performance but how do champions respond? They prevail," the victor stated in the ring as he was greeted with disapproval from the crowd.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to earn a 20th career victory.
Several boxing experts thought the challenger, 31, should have been awarded the victory but the British boxer experienced the second loss of his 28-match career.
Buatsi Earns Victory in Slow Affair
His career development has slowed in the past few years through promotional disputes and extended periods of inactivity.
Earlier forecast as the next star of British boxing, he now is positioned trying to achieve expectations - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with neither fighter willing to overcommit in a calculated initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was competing in only his second bout at the higher weight class.
By the halfway stage, Parker had kept it close, creating difficulties for the favorite, who operated with a protective stance to edge the better periods.
The crowd's patience wore thin amid constant clinching, with Parker going down multiple occasions during clinches.
The underdog ended stronger, but multiple periods were hard to judge. However, ex-champion Carl Frampton - working with the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just one round.
Buatsi moves on, but with the likes of power puncher Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Hatton Memorial Inspires Manchester Derby Fight
In the secondary fight, Arthur defeated Rea by close verdict in a terrific Manchester vs Manchester fight to capture the European light-heavyweight championship.
The stadium became quiet for a extremely emotional memorial before the fight as ten bells tolled in remembrance of local hero Hatton, who passed away aged 46 in recently.
It was the initial significant broadcast match card in the city since the passing of Hatton. As the final chime faded, the silence gave way to a shout of "there's just one Ricky Hatton".
The action inside the ropes equaled the sentiment. Arthur was knocked down by a powerful punch squarely on the chin in the early round, rising shakily to his position on the count of eight.
But the traditional red equipment of the fighter soon advanced again. Across the ring, Rea - in opposing blue - was marked up early, noticeable damage developing under his face as the duo exchanged hard punches.
The challenger, 27, connected with strong blows but the champion, 34, responded in kind with powerful upward punches as the action hardly diminished over the full distance.
The victor edged the decision with judges scorecards of 114-114, narrow lead and wider gap, but the two athletes were persistent and brave, everything their inspiration Hatton represented.
