UK light heavyweight Buatsi made a winning yet underwhelming debut to his career under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a competitive ten-round bout at the boxing arena.
But Parker found success, connecting with powerful single shots in a match where the techniques didn't complement each other, with frequent clinching spoiling the action.
Two judges had it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my greatest performance but what do champions do? They succeed," Buatsi stated in the ring as he was faced boos from the audience.
The British fighter bounced back after his initial pro loss - an epic battle with Callum Smith in last winter - to earn a 20th career victory.
Various analysts believed Parker, 31, merited the win but the contender experienced the second loss of his 28-bout professional journey.
The Champion Claims Triumph in Uneventful Affair
Buatsi's progress has plateaued in the past few years through promotional disputes and considerable time of inactivity.
Previously predicted as the future of British boxing, he now stands trying to realize his potential - perhaps in what feels like a last chance - under new promotional backing.
He opened tentatively, with the two boxers ready to take risks in a calculated opening few rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after breaking his hand mid-fight, was competing in only his second fight at the higher weight class.
By the middle rounds, Parker had made it competitive, making life awkward for Buatsi, who worked behind a protective stance to narrowly win the more effective stanzas.
The audience's tolerance wore thin amid constant clinching, with Parker slipping to the canvas multiple occasions during grappling.
Parker ended stronger, but several stanzas were challenging to assess. However, ex-champion Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the presence of hard hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Hatton Homage Inspires Manchester Derby Fight
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a excellent all-Manchester battle to capture the continental championship.
The stadium became quiet for a deeply poignant memorial ahead of the contest as ten bells rang in memory of local hero Hatton, who passed away 46 years old in recently.
It was the first major televised fight night in the urban center since Hatton's passing. As the concluding sound faded, the quiet gave way to a roar of "there's just one Ricky Hatton".
The competition within the ring matched the sentiment. Arthur was floored by a powerful punch squarely on the face in the early round, getting up unsteadily to his footing on the count of eight.
But the Manchester United-red equipment of the fighter soon came forward again. From the other corner, Rea - in rival City blue - was marked up early, noticeable damage forming under his orbital area as the fighters exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with effective uppercuts as the action hardly diminished over 12 rounds.
The victor narrowly won the decision with official scores of even score, close margin and wider gap, but the two athletes were relentless and full of heart, all the qualities their hero Hatton represented.
