UK light heavyweight Joshua Buatsi secured a victory yet disappointing debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a competitive 10-round contest at the Co-op Live Arena.
But Parker found success, landing some telling clean blows in a contest where the approaches never quite clicked, with constant grabbing disrupting the fight.
The scoring judges scored it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest display but what do champions do? They prevail," Buatsi said in the ring as he was faced negative reactions from the crowd.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in February - to earn a 20th pro success.
Various analysts believed the challenger, 31, deserved the victory but the contender suffered the second defeat of his 28-bout professional journey.
The Champion Claims Win in Uneventful Match
His career development has stalled in recent years through management issues and considerable time of inactivity.
Once tipped as the future of British boxing, he now is positioned trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers willing to be aggressive in a calculated early stages.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second fight at light heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for Buatsi, who utilized a solid defense to barely take the cleaner periods.
The audience's tolerance decreased amid constant clinching, with Parker falling to the floor multiple occasions during clinches.
Parker closed well, but many rounds were hard to judge. Although, ex-champion the boxing analyst - commentating on Dazn - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
Buatsi advances, but with the presence of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - based on this performance - still seems difficult.
Hatton Homage Inspires Local Rivalry Battle
In the co-main event, Arthur beat Bradley Rea by close verdict in a terrific local rivalry contest to capture the continental belt.
The arena became quiet for a profoundly moving homage ahead of the contest as ten bells rang in memory of Manchester's own Ricky Hatton, who died 46 years old in September.
It was the first major televised match card in the urban center since Hatton's death. As the last bell disappeared, the quiet gave way to a chant of "only one Hatton".
The competition within the ring matched the feeling. Arthur was floored by a powerful punch directly to the jaw in the early round, rising shakily to his footing on the count of eight.
But the traditional red equipment of Arthur soon came forward again. From the other corner, the opponent - in opposing blue - was injured early, heavy swelling developing under his face as the duo exchanged hard punches.
The challenger, 27, landed power punches but the champion, 34, responded in kind with effective uppercuts as the pace seldom decreased over 12 rounds.
Arthur edged the verdict with scoring tallies of even score, 115-113 and wider gap, but each competitor were determined and courageous, everything their inspiration Hatton stood for.
