British light-heavyweight Buatsi made a winning yet unimpressive start to his career under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a tight 10-round contest at the boxing arena.
But the challenger landed significant shots, landing some telling individual punches in a contest where the styles didn't complement each other, with excessive holding disrupting the action.
The scoring judges had it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my finest display but what defines champions? They succeed," the victor stated in the ring as he was faced disapproval from the crowd.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to earn a twentieth professional win.
Some ringside observers believed the challenger, 31, should have been awarded the decision but the British boxer endured the second setback of his 28-match professional journey.
The Champion Claims Victory in Uneventful Affair
The fighter's advancement has slowed in recent years through promotional disputes and extended periods of lack of fights.
Once tipped as the next star of the British fight scene, he now stands trying to realize his potential - maybe in what feels like a ultimate opportunity - under recent support.
He started carefully, with both competitors willing to be aggressive in a calculated initial rounds.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after damaging his hand mid-fight, was participating in his second appearance at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who utilized a tight guard to edge the cleaner periods.
The spectators' acceptance diminished amid frequent holding, with the challenger slipping to the canvas multiple occasions during clinches.
The underdog closed well, but several stanzas were challenging to assess. Although, former world champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor moves on, but with the presence of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - judging by this showing - still appears challenging.
Hatton Tribute Fuels All-Manchester Battle
In the co-main event, Arthur defeated Bradley Rea by close verdict in a excellent all-Manchester battle to capture the continental title.
The stadium fell silent for a deeply poignant tribute before the fight as 10 bells sounded in memory of Manchester's own Hatton, who died 46 years old in September.
It was the first major televised boxing event in the location since the passing of Hatton. As the last bell ended, the silence gave way to a shout of "only one Hatton".
The action during the bout equaled the sentiment. The eventual winner was floored by a powerful punch squarely on the face in the early round, standing uncertainly to his footing on the eight count.
But the red-colored shorts of the fighter soon came forward again. From the other corner, Rea - in opposing blue - was marked up soon, significant bruising forming under his face as the duo traded punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, responded in kind with effective uppercuts as the action rarely dropped over the full distance.
The victor narrowly won the verdict with scoring tallies of 114-114, close margin and clearer margin, but each competitor were determined and courageous, everything their idol the legend embodied.
