UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a majority decision in a tight 10-round fight at the boxing arena.
But the challenger had his moments, delivering effective single shots in a contest where the approaches never quite clicked, with frequent clinching marring the action.
Two judges judged it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest performance but what do champions do? They succeed," the victor stated in the arena as he was faced disapproval from the audience.
The British fighter bounced back after his maiden career setback - an thrilling contest with Callum Smith in last winter - to secure a 20th pro success.
Various analysts felt Parker, thirty-one, should have been awarded the win but the contender suffered the second defeat of his 28-fight professional journey.
The Champion Earns Victory in Slow Affair
Buatsi's progress has slowed in recent times through management issues and long spells of inactivity.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to realize his potential - maybe in what seems like a ultimate opportunity - under new promotional backing.
He opened tentatively, with both competitors willing to overcommit in a tentative initial rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in 2022 after breaking his hand during the bout, was making just his second fight at light heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for the favorite, who utilized a protective stance to narrowly win the cleaner stanzas.
The spectators' acceptance wore thin because of frequent holding, with the challenger going down various instances during close exchanges.
The underdog finished the stronger, but many rounds were hard to judge. Although, former world champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, giving Buatsi just only one stanza.
The victor progresses, but with the caliber of hard hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Homage Fuels Manchester Derby Fight
In the supporting bout, Arthur beat Rea by split-decision in a terrific local rivalry contest to win the European light heavyweight belt.
The arena grew hushed for a deeply poignant homage before the fight as a bell ceremony rang in memory of local hero Hatton, who died at age 46 in recently.
It was the premier televised match card in the city since Hatton's passing. As the final chime disappeared, the quiet gave way to a roar of "only one Hatton".
The competition inside the ropes reflected the sentiment. The eventual winner was sent to the canvas by a left hook flush on the chin in the initial stage, standing uncertainly to his position on the count of eight.
But the traditional red equipment of the fighter soon advanced again. Across the ring, Rea - in opposing blue - was injured soon, significant bruising developing under his eye as the pair exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with powerful upward punches as the pace seldom decreased over 12 rounds.
The victor barely secured the verdict with official scores of draw, 115-113 and wider gap, but the two athletes were persistent and courageous, exactly what their idol Hatton represented.
