British light-heavyweight Joshua Buatsi earned a win yet underwhelming start to his career under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a majority decision in a close ten-round fight at the Manchester venue.
But Parker landed significant shots, landing some telling single shots in a fight where the approaches never quite clicked, with frequent clinching spoiling the fight.
The officials judged it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my finest display but what do champions do? They win," Buatsi said in the arena as he was greeted with disapproval from the audience.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to secure a twentieth professional win.
Some ringside observers felt the challenger, thirty-one, deserved the decision but the British boxer suffered the second defeat of his 28-fight professional journey.
The Champion Claims Triumph in Uneventful Encounter
His career development has plateaued in recent years through contract problems and long spells of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to fulfil that early promise - perhaps in what feels like a ultimate opportunity - under recent support.
He opened tentatively, with the two boxers willing to take risks in a calculated early stages.
Parker, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was making just his second bout at light-heavyweight.
By the middle rounds, the underdog had made it competitive, making life awkward for Buatsi, who operated with a tight guard to barely take the better periods.
The crowd's patience wore thin during constant clinching, with Parker falling to the floor multiple occasions during grappling.
The underdog closed well, but many rounds were challenging to assess. Although, former world champion Carl Frampton - working with Dazn - had it significantly in favor for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - on this evidence - still seems difficult.
Hatton Tribute Fuels All-Manchester Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by split-decision in a outstanding Manchester vs Manchester fight to secure the European light heavyweight title.
The stadium grew hushed for a extremely emotional memorial ahead of the contest as ten bells rang in remembrance of Manchester's own Ricky Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the concluding sound faded, the stillness transitioned to a shout of "there's only one Ricky Hatton".
The competition within the ring reflected the emotion. The eventual winner was sent to the canvas by a powerful punch flush on the chin in the initial stage, rising shakily to his footing on the referee's count.
But the red-colored equipment of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was marked up soon, significant bruising forming under his eye as the duo traded punishing blows.
The challenger, 27, delivered effective strikes but Arthur, 34, matched the intensity with stinging uppercuts as the intensity rarely dropped over 12 rounds.
Arthur barely secured the result with official scores of even score, narrow lead and clearer margin, but the two athletes were determined and full of heart, everything their idol Hatton represented.
