British light-heavyweight Joshua Buatsi earned a win yet disappointing beginning to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a majority decision in a tight 10-round contest at the boxing arena.
But Parker had his moments, delivering effective clean blows in a match where the techniques failed to mesh, with constant grabbing spoiling the action.
Two judges had it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest display but what defines champions? They win," Buatsi said in the ringside as he was faced disapproval from the audience.
The British fighter got back to winning after his initial pro loss - an epic battle with his previous opponent in February - to earn a 20th pro success.
Some ringside observers felt Parker, 31, should have been awarded the win but the contender suffered the second loss of his 28-fight professional journey.
Buatsi Secures Triumph in Uneventful Encounter
Buatsi's progress has stalled in recent years through contract problems and considerable time of lack of fights.
Earlier forecast as the future of UK boxing, he now stands trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under recent support.
He began cautiously, with the two boxers willing to overcommit in a calculated opening few rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after suffering a hand injury during the bout, was participating in his second appearance at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for the favorite, who utilized a solid defense to narrowly win the more effective rounds.
The spectators' acceptance diminished amid regular grabbing, with the challenger going down multiple occasions during close exchanges.
The underdog finished the stronger, but several stanzas were hard to judge. Although, former world champion Carl Frampton - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
Buatsi moves on, but with the likes of power puncher Benavidez, and Russian star Bivol ruling the division, the road to world glory - based on this performance - still seems difficult.
Hatton Tribute Fuels Local Rivalry Fight
In the co-main event, Lyndon Arthur overcame Rea by close verdict in a outstanding Manchester vs Manchester contest to secure the European light-heavyweight title.
The stadium grew hushed for a extremely emotional memorial prior to the bout as ten bells sounded in memory of local hero Ricky Hatton, who passed away aged 46 in recently.
It was the initial significant broadcast fight night in the location since Hatton's death. As the final chime ended, the quiet gave way to a roar of "there's only one Hatton".
The competition inside the ropes equaled the sentiment. The eventual winner was sent to the canvas by a left hook squarely on the chin in the early round, rising shakily to his feet on the eight count.
But the red-colored shorts of the fighter soon came forward again. On the opposite side, the opponent - in opposing blue - was damaged early, noticeable damage developing under his orbital area as the pair landed powerful shots.
Rea, 27, landed power punches but the champion, 34, matched the intensity with effective uppercuts as the pace rarely dropped over 12 rounds.
Arthur barely secured the result with official scores of even score, close margin and wider gap, but both fighters were relentless and brave, all the qualities their idol Hatton embodied.
