Valverde brought on Arturo Vidal for Rakitic to have a bit more muscle in midfield, but Dortmund stayed on the front foot and they almost had a second when a Sancho striked looked goal-bound, but Ter Stegen's hand and the crossbar kept it a two-goal lead for the Catalan, which held until the final whistle.
"The coach always prepares us really well".
"Everyone has to take a good look at themselves, that's what we have to talk about, not about our coach", fumed Reus. "We have an fantastic team, most of the best players in the world, but we know we can perform way better, even if things aren't as bad as people are thinking".
Barcelona are top of Group F, a point ahead of Dortmund, and can make sure of a place in the last 16 with victory on Wednesday night.
"It is always hard to come here, and we always struggled here with 'Gladbach, but we will try to win and get a good start to the competition".
The Spaniards would also progress if Slavia Prague beat Inter Milan, or both the games end in a draw. "If we win, we'll be top of the group and of course that's what we want", Valverde said. Barcelona have quite a few injury concerns in defence, with Jordi Alba and Nelson Semedo ruled out, Clement Lenglet a doubt and Gerard Pique suspended.
There was more bad news, too, for Barcelona with the familiar sight of Ousmane Dembele sitting on the turf with an injury, requiring an early substitution of the former Dortmund man, who was replaced by Griezmann.
Arthur could also return, while fellow midfielder Ivan Rakitic is back after an Achilles problem - coming on at Leganes at the weekend.
Dortmund coach Lucien Favre, meanwhile, has seen his position come under scrutiny after inconsistent form.
Dortmund are struggling for results in the Bundesliga and a 3-3 draw at home against bottom club Paderborn on Friday left them with just two wins from their last eight league matches.
"We have to do a great job on Wednesday", Favre said.
"We have an wonderful team, most of the best players in the world, ” said De Jong".
"We will decide tomorrow".