UK light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a judges' verdict in a competitive ten-round contest at the Co-op Live Arena.
But the challenger found success, landing some telling individual punches in a contest where the techniques failed to mesh, with constant grabbing disrupting the fight.
The officials had it 96-94 in favor to the winner, with the third a even score.
"It wasn't my finest showing but how do champions respond? They win," Buatsi commented in the arena as he was met by boos from the crowd.
The British fighter returned to winning ways after his initial pro loss - an epic battle with his previous opponent in last winter - to earn a 20th pro success.
Several boxing experts believed Parker, thirty-one, should have been awarded the win but the Derbyshire fighter endured the second setback of his 28-fight career.
The Champion Claims Win in Dull Encounter
The fighter's advancement has slowed in the past few years through management issues and long spells of inactivity.
Earlier forecast as the rising talent of British boxing, he now stands trying to achieve expectations - perhaps in what appears to be a last chance - under new promotional backing.
He started carefully, with neither fighter prepared to be aggressive in a tentative opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after suffering a hand injury in the contest, was making just his second fight at light-heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a solid defense to edge the more effective rounds.
The audience's tolerance decreased amid regular grabbing, with Parker falling to the floor various instances during close exchanges.
Parker finished the stronger, but several stanzas were difficult to score. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
The victor progresses, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Homage Fuels Manchester Derby Battle
In the co-main event, Lyndon Arthur overcame Rea by split-decision in a excellent local rivalry fight to win the continental championship.
The venue fell silent for a deeply poignant homage before the fight as 10 bells sounded in memory of the city's native Ricky Hatton, who died 46 years old in last month.
It was the premier televised boxing event in the city since the passing of Hatton. As the concluding sound disappeared, the quiet became a roar of "there's only one Hatton".
The action during the bout reflected the feeling. The eventual winner was floored by a powerful punch squarely on the face in the second round, rising shakily to his position on the eight count.
But the traditional red shorts of Arthur soon pressed ahead again. From the other corner, Rea - in competitive blue - was marked up quickly, noticeable damage developing under his eye as the fighters traded hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with stinging uppercuts as the intensity hardly diminished over 12 rounds.
The victor narrowly won the decision with scoring tallies of even score, narrow lead and 115-112, but both fighters were determined and full of heart, everything their inspiration Hatton represented.
