It was another dramatic night in the Champions League as the teams set to feature in the Round of 16 became a little clearer.
Elsewhere Chelsea were involved in a thriller with Valencia and Liverpool were held against a team they have struggled to beat for two seasons now in Napoli.
However, after Kepa Arrizabalaga had saved Dani Parejo’s penalty, Wass’s cross flummoxed the Spanish international to give Valencia a lifeline.
Lille 0-2 Ajax
Four-time European champions Ajax have 10 points from five games, two more than Valencia and Chelsea who fought out a 2-2 draw in Spain earlier in the day.
Messi celebrated his anniversary in style by putting Barca two up before half-time, between laying on a pair of assists for Luis Suarez and Antoine Griezmann in a comfortable victory at Camp Nou.
Tomas Soucek levelled for Slavia from the penalty spot in the 37th minute after Stefan de Vrij had brought down striker Peter Olayinka in the box.
Polish referee Szymon Marciniak first ignored the foul and let play continue with Lukaku scoring on the counter-attack before seeing his goal chalked off as the video referee took centre stage.
Dejan Lovren’s header protected that proud unbeaten run, but the holders still need to get at least a point away to Salzburg on December 10 to secure their passage into the last 16.
Napoli remain a point behind Liverpool, but are well-placed to reach the knockout stages as they host winless Genk in two weeks’ time.