British light heavyweight Buatsi secured a victory yet underwhelming debut to his career under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a close ten-round fight at the Manchester venue.
But Parker found success, delivering effective clean blows in a contest where the styles never quite clicked, with frequent clinching disrupting the fight.
The scoring judges scored it 96-94 for to the winner, with the third a even score.
"It wasn't my greatest display but how do champions respond? They win," Buatsi commented in the ring as he was faced disapproval from the crowd.
The Londoner bounced back after his maiden career setback - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Various analysts believed Parker, thirty-one, merited the decision but the contender endured the second setback of his 28-bout career.
Buatsi Earns Triumph in Slow Match
His career development has slowed in the past few years through management issues and long spells of inactivity.
Earlier forecast as the future of British boxing, he now finds himself trying to achieve expectations - perhaps in what seems like a last chance - under new promotional backing.
He began cautiously, with the two boxers ready to be aggressive in a cagey initial rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after breaking his hand in the contest, was participating in his second fight at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for Buatsi, who utilized a tight guard to narrowly win the better periods.
The crowd's patience diminished amid regular grabbing, with the challenger going down several times during close exchanges.
The underdog ended stronger, but many rounds were difficult to score. Nevertheless, ex-champion the boxing analyst - working with the broadcast network - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor progresses, but with the presence of hard hitter Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Memorial Inspires All-Manchester Fight
In the secondary fight, Arthur overcame Bradley Rea by close verdict in a terrific local rivalry contest to secure the European light heavyweight championship.
The stadium grew hushed for a profoundly moving homage ahead of the contest as ten bells rang in remembrance of the city's native Hatton, who passed away at age 46 in last month.
It was the premier televised match card in the urban center since Hatton's passing. As the final chime disappeared, the silence transitioned to a shout of "there's just one Hatton".
The competition inside the ropes matched the feeling. The eventual winner was sent to the canvas by a significant blow squarely on the jaw in the second round, rising shakily to his footing on the count of eight.
But the red-colored equipment of the fighter soon advanced again. From the other corner, Rea - in competitive blue - was damaged soon, heavy swelling appearing under his eye as the fighters exchanged hard punches.
The challenger, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with stinging uppercuts as the pace hardly diminished over the full distance.
The victor barely secured the verdict with scoring tallies of even score, narrow lead and wider gap, but each competitor were persistent and brave, everything their idol Hatton embodied.
