UK light-heavyweight Joshua Buatsi made a winning yet unimpressive beginning to his career under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive 10-round bout at the Co-op Live Arena.
But Parker found success, connecting with powerful individual punches in a contest where the styles failed to mesh, with constant grabbing marring the fight.
Two judges scored it 96-94 for to the winner, with the third a 95-95.
"It wasn't my finest performance but what do champions do? They succeed," the victor said in the ring as he was greeted with boos from the crowd.
The Londoner returned to winning ways after his initial pro loss - an epic battle with his previous opponent in February - to earn a 20th pro success.
Some ringside observers believed Parker, thirty-one, deserved the decision but the Derbyshire fighter suffered the second setback of his 28-match career.
The Champion Earns Win in Uneventful Match
His career development has stalled in the past few years through contract problems and considerable time of inactivity.
Once tipped as the future of the British fight scene, he now finds himself trying to realize his potential - maybe in what appears to be a last chance - under new promotional backing.
He started carefully, with the two boxers ready to be aggressive in a cagey opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after suffering a hand injury in the contest, was making just his second appearance at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to narrowly win the cleaner rounds.
The crowd's patience diminished because of frequent holding, with the challenger going down various instances during grappling.
Parker ended stronger, but multiple periods were challenging to assess. However, former world champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, giving Buatsi just one round.
The victor moves on, but with the presence of hard hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Hatton Homage Inspires Manchester Derby Fight
In the supporting bout, Arthur beat Rea by split-decision in a terrific all-Manchester fight to secure the European light heavyweight title.
The venue became quiet for a extremely emotional tribute prior to the bout as 10 bells tolled in remembrance of the city's native Ricky Hatton, who died aged 46 in last month.
It was the premier televised boxing event in the location since Hatton's death. As the last bell disappeared, the stillness gave way to a chant of "there's just one Ricky Hatton".
The competition within the ring equaled the feeling. Arthur was floored by a left hook flush on the jaw in the second round, standing uncertainly to his position on the eight count.
But the Manchester United-red shorts of the fighter soon pressed ahead again. Across the ring, the opponent - in rival City blue - was damaged quickly, significant bruising appearing under his eye as the duo exchanged punishing blows.
Rea, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with stinging uppercuts as the action rarely dropped over the full distance.
Arthur narrowly won the decision with scoring tallies of even score, close margin and clearer margin, but the two athletes were persistent and courageous, exactly what their idol Hatton embodied.
