UK light-heavyweight Joshua Buatsi made a winning yet underwhelming debut to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a judges' verdict in a competitive ten-round contest at the boxing arena.
But the challenger had his moments, connecting with powerful single shots in a fight where the styles never quite clicked, with frequent clinching marring the action.
The officials scored it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest performance but what do champions do? They succeed," the victor commented in the ring as he was greeted with boos from the audience.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to claim a 20th career victory.
Some ringside observers felt Parker, 31, merited the win but the British boxer suffered the second setback of his 28-bout professional journey.
Buatsi Secures Victory in Dull Match
Buatsi's progress has stalled in the past few years through management issues and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under recent support.
He started carefully, with the two boxers ready to be aggressive in a calculated initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was making just his second fight at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for Buatsi, who worked behind a protective stance to edge the better rounds.
The spectators' acceptance diminished during regular grabbing, with Parker falling to the floor multiple occasions during clinches.
Parker closed well, but multiple periods were difficult to score. However, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, giving Buatsi just only one stanza.
The victor progresses, but with the caliber of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - judging by this showing - still looks steep.
Hatton Tribute Fuels All-Manchester Battle
In the secondary fight, Arthur defeated Bradley Rea by split-decision in a terrific local rivalry battle to win the European light-heavyweight title.
The venue fell silent for a deeply poignant memorial prior to the bout as 10 bells sounded in honor of local hero Hatton, who passed away 46 years old in recently.
It was the first major televised boxing event in the location since Hatton's death. As the final chime ended, the quiet became a roar of "there's only one Hatton".
The fighting during the bout matched the sentiment. Arthur was knocked down by a left hook squarely on the face in the initial stage, standing uncertainly to his position on the count of eight.
But the red-colored attire of Arthur soon advanced again. Across the ring, Rea - in opposing blue - was injured soon, heavy swelling appearing under his eye as the duo landed hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with effective uppercuts as the action rarely dropped over 12 rounds.
The victor barely secured the result with official scores of 114-114, close margin and 115-112, but both fighters were determined and full of heart, all the qualities their idol the legend stood for.
