Goals from Kylian Mbappe, Edinson Cavani, Neymar and Angel Di Maria handed Unai Emery's men a comprehensive away victory at the Constant Vanden Stock Stadium.
Mbappe unsettled the hosts after he blasted a strike past Matz Sels in the third minute.
Onyekuru had two chances in quick successions to level the tie for his side but Alphonse Areola was at his best to deny him. The first; a firm header off a right-wing cross which was calmly gathered by the French youngster and it was followed by an impressive save when the former Eupen man was played through on goal.
In the 44th minute, Cavani benefitted from a Mbappe assist to double the Parisians’ lead while Neymar netted the third for Unai Emery’s men with a brilliant low freekick in the 66th minute.
Onyekuru, who was a constant menace for Brazilian right back Dani Alves, almost pulled one back for the White and Purple but his effort struck the bar before substitute Angel Di Maria sealed victory for the French Ligue 1 outfit.
Despite his commanding performance which saw him last for the entire duration, the 20-year-old was cautioned in the 55th minute.
With this loss, Hein Vanhaezebrouck’s side are still rooted to the bottom of Group B after failing to get any point from three games played so far in the European club elite competition.