British light-heavyweight Joshua Buatsi made a winning yet disappointing debut to life under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a close 10-round bout at the Co-op Live Arena.
But the challenger found success, delivering effective individual punches in a contest where the techniques didn't complement each other, with excessive holding marring the contest.
The scoring judges scored it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest performance but what defines champions? They succeed," Buatsi stated in the arena as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to earn a twentieth professional win.
Some ringside observers felt the challenger, 31, should have been awarded the victory but the contender suffered the second loss of his 28-fight career.
Buatsi Secures Triumph in Slow Affair
Buatsi's progress has stalled in recent times through promotional disputes and long spells of inactivity.
Once tipped as the next star of the British fight scene, he now stands trying to realize his potential - maybe in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with neither fighter prepared to overcommit in a cagey opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after suffering a hand injury during the bout, was making just his second appearance at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for the favorite, who worked behind a tight guard to narrowly win the better rounds.
The audience's tolerance wore thin amid frequent holding, with Parker going down various instances during grappling.
Parker ended stronger, but several stanzas were difficult to score. Nevertheless, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
Buatsi advances, but with the presence of power puncher Benavidez, and Russian star Bivol leading the category, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Homage Fuels All-Manchester Fight
In the supporting bout, Lyndon Arthur overcame Rea by close verdict in a terrific all-Manchester battle to secure the European light heavyweight championship.
The arena grew hushed for a deeply poignant tribute ahead of the contest as 10 bells tolled in honor of local hero Hatton, who died 46 years old in September.
It was the first major televised match card in the location since Hatton's passing. As the last bell ended, the stillness transitioned to a roar of "there's only one Hatton".
The fighting within the ring equaled the emotion. Arthur was sent to the canvas by a significant blow flush on the jaw in the early round, rising shakily to his position on the eight count.
But the Manchester United-red shorts of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was injured quickly, heavy swelling developing under his eye as the duo traded hard punches.
Rea, 27, delivered effective strikes but the champion, 34, fought fire with fire with effective uppercuts as the pace hardly diminished over the full distance.
Arthur barely secured the verdict with official scores of 114-114, 115-113 and clearer margin, but both fighters were persistent and brave, exactly what their idol Hatton stood for.
