UK light heavyweight Joshua Buatsi secured a victory yet disappointing beginning to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a judges' verdict in a competitive ten-round contest at the Manchester venue.
But Parker landed significant shots, landing some telling individual punches in a match where the techniques never quite clicked, with constant grabbing disrupting the action.
The officials had it 96-94 to the winner, with the third a 95-95.
"It wasn't my finest performance but what do champions do? They prevail," the victor commented in the ringside as he was met by negative reactions from the spectators.
The Londoner bounced back after his maiden career setback - an memorable fight with Callum Smith in last winter - to claim a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, merited the decision but the British boxer experienced the second setback of his 28-fight career.
Buatsi Earns Triumph in Uneventful Encounter
The fighter's advancement has slowed in recent years through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of British boxing, he now stands trying to achieve expectations - maybe in what feels like a last chance - under recent support.
He started carefully, with both competitors prepared to take risks in a cagey opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was competing in only his second bout at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who operated with a tight guard to barely take the cleaner rounds.
The crowd's patience wore thin during constant clinching, with the challenger going down various instances during grappling.
The underdog finished the stronger, but many rounds were hard to judge. Although, ex-champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, giving Buatsi just a single round.
The victor progresses, but with the caliber of heavy hitter Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - on this evidence - still appears challenging.
Hatton Memorial Inspires Manchester Derby Battle
In the supporting bout, Lyndon Arthur defeated Rea by close verdict in a excellent local rivalry battle to capture the European light heavyweight belt.
The venue became quiet for a profoundly moving memorial ahead of the contest as ten bells rang in memory of local hero Ricky Hatton, who succumbed aged 46 in last month.
It was the premier televised boxing event in the location since Hatton's passing. As the concluding sound faded, the stillness became a shout of "there's only one Hatton".
The action inside the ropes reflected the sentiment. The eventual winner was floored by a significant blow squarely on the chin in the second round, standing uncertainly to his footing on the referee's count.
But the traditional red shorts of the fighter soon pressed ahead again. From the other corner, Rea - in competitive blue - was injured soon, noticeable damage developing under his eye as the pair traded powerful shots.
Rea, 27, landed power punches but the champion, 34, matched the intensity with effective uppercuts as the pace hardly diminished over the full distance.
Arthur edged the decision with official scores of draw, 115-113 and 115-112, but the two athletes were relentless and brave, everything their inspiration Hatton stood for.
