UK light heavyweight Joshua Buatsi secured a victory yet underwhelming start to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a close ten-round contest at the Manchester venue.
But the challenger landed significant shots, connecting with powerful individual punches in a fight where the techniques didn't complement each other, with excessive holding disrupting the action.
The scoring judges scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my best performance but what defines champions? They succeed," the victor said in the ringside as he was met by disapproval from the spectators.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to claim a 20th pro success.
Various analysts believed the challenger, thirty-one, deserved the win but the contender experienced the second setback of his 28-match career.
Buatsi Secures Victory in Uneventful Affair
The fighter's advancement has slowed in the past few years through contract problems and considerable time of inactivity.
Previously predicted as the next star of the British fight scene, he now stands trying to realize his potential - possibly in what seems like a last chance - under recent support.
He began cautiously, with both competitors ready to take risks in a cagey opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in 2022 after breaking his hand in the contest, was making just his second appearance at light-heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for the favorite, who operated with a protective stance to barely take the more effective stanzas.
The crowd's patience wore thin because of regular grabbing, with the challenger falling to the floor multiple occasions during grappling.
The underdog closed well, but multiple periods were difficult to score. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Russian champion Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Hatton Homage Motivates Manchester Derby Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by split-decision in a terrific local rivalry fight to win the European light heavyweight belt.
The venue grew hushed for a deeply poignant tribute prior to the bout as 10 bells rang in remembrance of the city's native Hatton, who died 46 years old in recently.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the last bell faded, the quiet gave way to a roar of "there's just one Hatton".
The fighting inside the ropes equaled the sentiment. Arthur was knocked down by a significant blow directly to the jaw in the early round, rising shakily to his footing on the referee's count.
But the Manchester United-red attire of the fighter soon pressed ahead again. From the other corner, Rea - in opposing blue - was marked up early, noticeable damage appearing under his eye as the duo exchanged powerful shots.
The challenger, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the pace hardly diminished over twelve rounds.
The victor edged the result with official scores of even score, close margin and 115-112, but the two athletes were relentless and brave, exactly what their hero Hatton stood for.
