British light heavyweight Buatsi secured a victory yet unimpressive debut to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a judges' verdict in a tight 10-round fight at the Manchester venue.
But the challenger found success, connecting with powerful individual punches in a fight where the approaches never quite clicked, with frequent clinching marring the action.
The officials scored it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my greatest display but what do champions do? They win," Buatsi commented in the ring as he was met by disapproval from the crowd.
The Londoner got back to winning after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a 20th career victory.
Various analysts thought the challenger, 31, merited the win but the Derbyshire fighter experienced the second setback of his 28-fight professional journey.
The Champion Claims Victory in Slow Encounter
The fighter's advancement has slowed in the past few years through contract problems and long spells of inactivity.
Previously predicted as the future of UK boxing, he now stands trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with the two boxers ready to take risks in a cagey opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in two years ago after damaging his hand mid-fight, was participating in his second bout at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for Buatsi, who operated with a tight guard to narrowly win the more effective rounds.
The spectators' acceptance decreased amid regular grabbing, with the challenger falling to the floor various instances during close exchanges.
Parker closed well, but multiple periods were difficult to score. However, ex-champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - based on this performance - still looks steep.
Hatton Tribute Fuels Manchester Derby Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding all-Manchester contest to secure the European light-heavyweight belt.
The stadium became quiet for a extremely emotional memorial ahead of the contest as ten bells sounded in memory of local hero Hatton, who passed away at age 46 in September.
It was the first major televised fight night in the location since Hatton's passing. As the final chime faded, the quiet transitioned to a roar of "only one Ricky Hatton".
The competition within the ring matched the sentiment. The eventual winner was floored by a left hook directly to the chin in the initial stage, getting up unsteadily to his footing on the count of eight.
But the traditional red shorts of the fighter soon pressed ahead again. Across the ring, Rea - in opposing blue - was damaged quickly, noticeable damage appearing under his orbital area as the fighters landed punishing blows.
The challenger, 27, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the pace seldom decreased over the full distance.
The victor narrowly won the result with scoring tallies of even score, narrow lead and clearer margin, but both fighters were determined and courageous, everything their inspiration the legend represented.
