British light heavyweight Buatsi secured a victory yet unimpressive beginning to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a split decision in a competitive ten-round contest at the boxing arena.
But the challenger had his moments, landing some telling clean blows in a contest where the approaches didn't complement each other, with excessive holding disrupting the action.
Two judges had it 96-94 for to the winner, with the third a even score.
"It wasn't my finest display but what defines champions? They prevail," the victor said in the ring as he was greeted with 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 secure a 20th pro success.
Some ringside observers believed the challenger, 31, should have been awarded the victory but the British boxer experienced the second setback of his 28-match career.
Buatsi Earns Victory in Dull Match
The fighter's advancement has stalled in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the next star of British boxing, he now finds himself trying to fulfil that early promise - possibly in what feels like a last chance - under new promotional backing.
He began cautiously, with neither fighter willing to take risks in a tentative early stages.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second bout at the higher weight class.
By the halfway stage, Parker had stayed in contention, causing problems for Buatsi, who worked behind a solid defense to narrowly win the better stanzas.
The audience's tolerance diminished because of constant clinching, with Parker falling to the floor various instances during close exchanges.
The underdog closed well, but many rounds were hard to judge. However, former world champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
Buatsi moves on, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - on this evidence - still appears challenging.
Ricky Hatton Homage Fuels All-Manchester Fight
In the co-main event, Arthur overcame Rea by close verdict in a outstanding Manchester vs Manchester fight to secure the European light-heavyweight championship.
The stadium grew hushed for a profoundly moving memorial prior to the bout as 10 bells tolled in honor of Manchester's own Hatton, who died aged 46 in September.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the final chime faded, the silence became a shout of "only one Hatton".
The action during the bout equaled the sentiment. Arthur was floored by a left hook directly to the jaw in the second round, getting up unsteadily to his position on the referee's count.
But the Manchester United-red attire of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was marked up early, noticeable damage forming under his orbital area as the pair traded punishing blows.
The challenger, 27, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the intensity seldom decreased over twelve rounds.
The victor narrowly won the verdict with scoring tallies of draw, close margin and 115-112, but both fighters were relentless and full of heart, exactly what their inspiration the legend represented.
