UK light heavyweight Joshua Buatsi secured a victory yet disappointing start to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a majority decision in a close ten-round fight at the Co-op Live Arena.
But Parker found success, landing some telling clean blows in a contest where the styles failed to mesh, with excessive holding spoiling the contest.
The officials had it 96-94 for to the winner, with the final judge a even score.
"It wasn't my greatest display but what do champions do? They win," the victor said in the arena as he was faced disapproval from the spectators.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to secure a 20th career victory.
Some ringside observers believed the challenger, thirty-one, deserved the win but the British boxer experienced the second defeat of his 28-bout professional journey.
The Champion Secures Triumph in Uneventful Encounter
His career development has slowed in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the next star of the British fight scene, he now is positioned trying to realize his potential - perhaps in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with both competitors prepared to be aggressive in a calculated early stages.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was competing in only his second appearance at light-heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who worked behind a tight guard to barely take the cleaner rounds.
The audience's tolerance decreased during regular grabbing, with the challenger going down several times during close exchanges.
The underdog finished the stronger, but many rounds were challenging to assess. However, ex-champion the boxing analyst - working with the broadcast network - had it significantly in favor for Parker, giving Buatsi just only one stanza.
The victor progresses, but with the likes of heavy hitter David Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Hatton Homage Fuels Local Rivalry Battle
In the secondary fight, Arthur defeated Bradley Rea by divided decision in a outstanding all-Manchester contest to win the European light heavyweight championship.
The stadium became quiet for a extremely emotional memorial before the fight as ten bells rang in remembrance of local hero Hatton, who succumbed aged 46 in September.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the final chime disappeared, the silence transitioned to a roar of "there's just one Hatton".
The competition within the ring equaled the feeling. Arthur was sent to the canvas by a significant blow squarely on the face in the second round, getting up unsteadily to his footing on the count of eight.
But the traditional red equipment of the fighter soon came forward again. Across the ring, the opponent - in competitive blue - was marked up soon, heavy swelling appearing under his orbital area as the pair traded punishing blows.
Rea, 27, delivered effective strikes but Arthur, 34, matched the intensity with stinging uppercuts as the action hardly diminished over twelve rounds.
Arthur barely secured the decision with judges scorecards of even score, narrow lead and clearer margin, but the two athletes were persistent and courageous, exactly what their hero Hatton represented.
