UK light heavyweight Joshua Buatsi earned a win yet unimpressive beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a competitive 10-round bout at the boxing arena.
But the challenger landed significant shots, landing some telling individual punches in a contest where the styles never quite clicked, with frequent clinching disrupting the action.
The officials judged it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my best showing but what defines champions? They prevail," the victor commented in the arena as he was met by disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an memorable fight with his previous opponent in February - to secure a 20th career victory.
Some ringside observers believed Parker, 31, deserved the victory but the British boxer endured the second defeat of his 28-bout career.
The Champion Claims Victory in Uneventful Encounter
The fighter's advancement has plateaued in recent times through contract problems and considerable time of inactivity.
Earlier forecast as the future of UK boxing, he now stands trying to realize his potential - maybe in what feels like a last chance - under recent support.
He started carefully, with the two boxers willing to overcommit in a cagey early stages.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after breaking his hand mid-fight, was making just his second bout at the higher weight class.
By the halfway stage, Parker had made it competitive, creating difficulties for the favorite, who worked behind a solid defense to barely take the cleaner rounds.
The crowd's patience wore thin during constant clinching, with Parker going down several times during grappling.
Parker closed well, but several stanzas were difficult to score. Nevertheless, former world champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, giving Buatsi just one round.
Buatsi progresses, but with the likes of hard hitter Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Memorial Inspires Local Rivalry Contest
In the supporting bout, Arthur overcame Bradley Rea by split-decision in a terrific Manchester vs Manchester fight to secure the continental championship.
The stadium became quiet for a extremely emotional memorial prior to the bout as ten bells sounded in remembrance of the city's native Ricky Hatton, who died at age 46 in recently.
It was the first major televised boxing event in the city since Hatton's passing. As the concluding sound faded, the quiet transitioned to a shout of "there's just one Ricky Hatton".
The fighting during the bout reflected the feeling. The eventual winner was sent to the canvas by a significant blow flush on the face in the initial stage, rising shakily to his footing on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in opposing blue - was injured soon, significant bruising appearing under his eye as the pair exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with stinging uppercuts as the intensity rarely dropped over twelve rounds.
The victor narrowly won the decision with scoring tallies of 114-114, narrow lead and 115-112, but the two athletes were relentless and brave, everything their idol Hatton represented.
