The Germans have scored 12 goals in their last three league games alone and look to be hitting top form at the right time.
"We are brimming with confidence, the atmosphere within the team is great," Dortmund coach Thomas Tuchel said after his team crushed Bayer Leverkusen 6-2 in the Bundesliga on Saturday.
"We are focussed, we take it step by step, and that is a great development for the team and a really good phase for us at the moment."
Dortmund also scored a record-breaking 21 goals in the Champions League group phase, but it could not keep up the streak in Lisbon last month, when they squandered a bagful of chances and a penalty to lose 1-0.
Bundesliga leading scorer Pierre-Emerick Aubameyang, who missed most of those chances and saw his spot kick saved, has since rediscovered his scoring form, netting twice against Leverkusen.
"We have been creating chances and huge scoring opportunities for weeks now," Tuchel said.
However, he will lack versatile attacking midfielder Reus, who suffered a thigh muscle injury on Saturday and was ruled out for a month.
"Marco has been extremely consistent for the past weeks ... and it is a big blow for us that he is not playing on Wednesday," Tuchel said.
Mario Goetze will also be missing, with the Germany midfielder sidelined since late last month with a metabolic disorder.
Tuchel has enough firepower left and can also count on his in-form youngsters, including teenagers Christian Pulisic and Ousmane Dembele, both of whom were on target on Saturday.
The Portuguese are equally deadly up front and poised to reach the last eight for the third time in six season.
Benfica are also in form, having won their last seven matches in all competitions. Striker Kostas Mitroglou, who scored the winner in the first leg, has grabbed 18 goals in his last 17 appearances.
They are top of the league, a point ahead of rivals Porto, and through to the Portuguese Cup final.
"We are not worried about others," said Benfica coach Rui Vitoria. "Our focus is on us and what we have to do. Every game at this stage is a final for us. The pressure on Benfica is normal and it has to be this way."
(Reporting by Karolos Grohmann, editing by Larry King)
