British light heavyweight Joshua Buatsi made a winning yet unimpressive debut to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a majority decision in a tight ten-round bout at the Co-op Live Arena.
But Parker landed significant shots, delivering effective single shots in a fight where the styles didn't complement each other, with constant grabbing disrupting the action.
The officials judged it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my finest showing but what defines champions? They win," Buatsi commented in the ring as he was met by negative reactions from the spectators.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Some ringside observers thought Parker, thirty-one, merited the decision but the British boxer suffered the second setback of his 28-fight career.
The Champion Claims Triumph in Uneventful Affair
Buatsi's progress has stalled in recent years through management issues and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to realize his potential - perhaps in what seems like a last chance - under new promotional backing.
He started carefully, with the two boxers prepared to be aggressive in a cagey opening few rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after breaking his hand during the bout, was competing in only his second appearance at the higher weight class.
By the middle rounds, the underdog had kept it close, making life awkward for the favorite, who worked behind a tight guard to narrowly win the more effective stanzas.
The spectators' acceptance wore thin amid regular grabbing, with the challenger falling to the floor various instances during grappling.
The underdog finished the stronger, but many rounds were difficult to score. Although, previous titleholder Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
The victor moves on, but with the caliber of hard hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Memorial Inspires Local Rivalry Fight
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a excellent Manchester vs Manchester battle to capture the European light heavyweight championship.
The stadium fell silent for a extremely emotional tribute prior to the bout as ten bells tolled in remembrance of Manchester's own Ricky Hatton, who succumbed 46 years old in recently.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the concluding sound faded, the quiet transitioned to a shout of "there's only one Ricky Hatton".
The competition during the bout reflected the feeling. Arthur was floored by a significant blow flush on the face in the early round, standing uncertainly to his footing on the eight count.
But the traditional red equipment of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was injured quickly, noticeable damage appearing under his eye as the fighters traded hard punches.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with effective uppercuts as the pace rarely dropped over twelve rounds.
Arthur barely secured the verdict with scoring tallies of draw, close margin and wider gap, but the two athletes were relentless and courageous, all the qualities their idol Hatton embodied.
