British light-heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a competitive 10-round fight at the boxing arena.
But Parker had his moments, connecting with powerful clean blows in a contest where the approaches didn't complement each other, with constant grabbing disrupting the contest.
The scoring judges scored it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my best display but what defines champions? They succeed," Buatsi said in the ringside as he was faced boos from the crowd.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to claim a 20th pro success.
Some ringside observers believed the challenger, 31, should have been awarded the victory but the Derbyshire fighter experienced the second defeat of his 28-bout professional journey.
The Champion Earns Triumph in Uneventful Match
The fighter's advancement has plateaued in recent years through management issues and extended periods of inactivity.
Once tipped as the next star of the British fight scene, he now finds himself trying to realize his potential - possibly in what seems like a final roll of the dice - under fresh management.
He began cautiously, with neither fighter prepared to overcommit in a cagey initial rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after suffering a hand injury during the bout, was competing in only his second fight at the higher weight class.
By the middle rounds, the underdog had kept it close, causing problems for Buatsi, who utilized a tight guard to barely take the more effective rounds.
The crowd's patience decreased during regular grabbing, with Parker going down several times during close exchanges.
The underdog ended stronger, but many rounds were hard to judge. Nevertheless, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the presence of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Homage Inspires All-Manchester Fight
In the supporting bout, Lyndon Arthur defeated Bradley Rea by split-decision in a terrific local rivalry contest to secure the continental championship.
The arena became quiet for a deeply poignant tribute ahead of the contest as 10 bells rang in memory of local hero Ricky Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the concluding sound faded, the stillness became a shout of "there's just one Ricky Hatton".
The fighting during the bout matched the sentiment. Arthur was sent to the canvas by a powerful punch flush on the chin in the initial stage, rising shakily to his footing on the eight count.
But the traditional red equipment of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was marked up quickly, noticeable damage developing under his eye as the pair traded hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with powerful upward punches as the intensity hardly diminished over the full distance.
Arthur edged the verdict with judges scorecards of even score, close margin and clearer margin, but the two athletes were relentless and brave, exactly what their hero Hatton embodied.
