UK light-heavyweight Joshua Buatsi made a winning yet unimpressive start to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a close 10-round fight at the Manchester venue.
But the challenger found success, connecting with powerful single shots in a fight where the styles didn't complement each other, with constant grabbing marring the contest.
Two judges had it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my best display but how do champions respond? They succeed," the victor stated in the ringside as he was greeted with boos from the audience.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Some ringside observers believed Parker, 31, deserved the decision but the Derbyshire fighter suffered the second loss of his 28-match career.
The Champion Secures Win in Uneventful Match
His career development has plateaued in recent years through promotional disputes and considerable time of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to realize his potential - maybe in what appears to be a final roll of the dice - under new promotional backing.
He began cautiously, with both competitors prepared to overcommit in a cagey early stages.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was participating in his second bout at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for the favorite, who worked behind a protective stance to barely take the cleaner stanzas.
The spectators' acceptance diminished because of constant clinching, with Parker going down several times during close exchanges.
The underdog finished the stronger, but many rounds were challenging to assess. However, previous titleholder the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, giving Buatsi just a single round.
Buatsi progresses, but with the caliber of hard hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Memorial Inspires Manchester Derby Battle
In the co-main event, Arthur overcame Rea by close verdict in a terrific Manchester vs Manchester contest to win the European light heavyweight belt.
The venue grew hushed for a extremely emotional memorial before the fight as ten bells rang in memory of Manchester's own Hatton, who died 46 years old in recently.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the last bell faded, the stillness became a shout of "there's just one Ricky Hatton".
The action during the bout equaled the emotion. The eventual winner was floored by a significant blow flush on the jaw in the second round, getting up unsteadily to his position on the count of eight.
But the Manchester United-red equipment of the fighter soon advanced again. From the other corner, Rea - in competitive blue - was damaged quickly, noticeable damage forming under his orbital area as the duo traded punishing blows.
The challenger, 27, connected with strong blows but Arthur, thirty-four, responded in kind with powerful upward punches as the pace rarely dropped over 12 rounds.
Arthur narrowly won the verdict with official scores of even score, narrow lead and 115-112, but the two athletes were determined and brave, everything their inspiration Hatton stood for.
