British light heavyweight Buatsi made a winning yet underwhelming beginning to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a close 10-round bout at the Manchester venue.
But the challenger landed significant shots, delivering effective single shots in a contest where the techniques failed to mesh, with excessive holding marring the action.
The officials judged it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my greatest performance but what defines champions? They win," the victor said in the ring as he was faced negative reactions from the crowd.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in February - to secure a 20th career victory.
Several boxing experts believed Parker, thirty-one, should have been awarded the win but the contender suffered the second loss of his 28-fight career.
The Champion Claims Victory in Dull Affair
The fighter's advancement has slowed in the past few years through contract problems and extended periods of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to realize his potential - perhaps in what seems like a last chance - under fresh management.
He began cautiously, with neither fighter ready to take risks in a cagey initial rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after damaging his hand during the bout, was making just his second appearance at light heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who worked behind a tight guard to edge the cleaner stanzas.
The crowd's patience diminished during frequent holding, with the challenger slipping to the canvas several times during clinches.
The underdog ended stronger, but many rounds were challenging to assess. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
Buatsi progresses, but with the presence of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - based on this performance - still looks steep.
Hatton Homage Inspires All-Manchester Fight
In the co-main event, Arthur beat Rea by split-decision in a excellent local rivalry contest to win the continental belt.
The stadium grew hushed for a extremely emotional tribute prior to the bout as 10 bells rang in memory of local hero Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the concluding sound faded, the quiet became a shout of "only one Ricky Hatton".
The competition inside the ropes matched the emotion. Arthur was sent to the canvas by a left hook squarely on the jaw in the early round, standing uncertainly to his feet on the referee's count.
But the traditional red equipment of Arthur soon advanced again. Across the ring, Rea - in competitive blue - was marked up early, noticeable damage appearing under his orbital area as the duo exchanged punishing blows.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the pace hardly diminished over the full distance.
Arthur edged the result with official scores of 114-114, 115-113 and 115-112, but both fighters were relentless and courageous, everything their hero the legend embodied.
