UK light heavyweight Joshua Buatsi secured a victory yet disappointing debut to his career under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a split decision in a tight ten-round contest at the boxing arena.
But the challenger landed significant shots, connecting with powerful individual punches in a contest where the approaches failed to mesh, with constant grabbing spoiling the fight.
Two judges had it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my finest display but what defines champions? They succeed," the victor stated in the ring as he was met by disapproval from the audience.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to claim a 20th career victory.
Various analysts felt the challenger, 31, deserved the decision but the Derbyshire fighter suffered the second defeat of his 28-fight career.
Buatsi Earns Win in Dull Affair
His career development has slowed in the past few years through management issues and extended periods of lack of fights.
Previously predicted as the future of the British fight scene, he now stands trying to realize his potential - maybe in what feels like a last chance - under recent support.
He started carefully, with neither fighter willing to overcommit in a cagey opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after damaging his hand during the bout, was making just his second bout at light heavyweight.
By the middle rounds, Parker had stayed in contention, making life awkward for the favorite, who worked behind a protective stance to narrowly win the cleaner rounds.
The spectators' acceptance decreased during frequent holding, with the challenger falling to the floor various instances during grappling.
Parker closed well, but several stanzas were hard to judge. Nevertheless, former world champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, awarding Buatsi just one round.
The victor advances, but with the caliber of power puncher David Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Hatton Memorial Fuels Local Rivalry Battle
In the secondary fight, Arthur defeated Rea by close verdict in a outstanding Manchester vs Manchester fight to capture the European light-heavyweight belt.
The venue grew hushed for a deeply poignant homage prior to the bout as 10 bells rang in honor of the city's native Hatton, who succumbed aged 46 in recently.
It was the premier televised match card in the location since Hatton's passing. As the final chime ended, the quiet transitioned to a roar of "there's only one Hatton".
The action inside the ropes matched the sentiment. The eventual winner was floored by a significant blow directly to the jaw in the second round, getting up unsteadily to his position on the count of eight.
But the red-colored attire of Arthur soon came forward again. On the opposite side, the opponent - in competitive blue - was damaged early, significant bruising developing under his face as the pair exchanged powerful shots.
Rea, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the intensity rarely dropped over the full distance.
The victor narrowly won the result with official scores of even score, narrow lead and clearer margin, but both fighters were determined and courageous, exactly what their hero the legend stood for.
