Inter struck twice in the second half through Nicolo Barella (26) and Romelu Lukaku (29) to secure a 2-0 win in the first leg in Portugal last week, ending Benfica's unbeaten run in the Champions League this season after six wins and two draws.
"We had our chances last week, but didn't make the most of them. We need motivation, sharp minds and to leave all emotions off the pitch. It is time to prove we belong here, otherwise we’ll be out of the Champions League," Schmidt told reporters on Tuesday.
"An early goal could change the whole tie, just as the one we almost got at the last second of the first leg," Schmidt added, stressing the need for his side to go on the offensive early.
"I’ve seen my team play at their best and there were big margins of improvement from the performance I saw last week."
The German manager pointed out that his side had several chances in the first leg, but lacked balance in their approach.
"We've created several opportunities, but what we need is tactical balance, within our more offensive style of play," he said.
Benfica head into the match after three consecutive losses in all competitions, but they remain top of the Portuguese Primeira Liga, four points ahead of second-placed Porto.
"It is very strange to have lost three games in a row in all competitions and totally unexpected, especially as we had lost only one before this run of results," Schmidt said.
"The players did fantastic things all season and that means something. Even if Inter won 2-0, the statistics show it was a fairly balanced match and we had our chances too. It’s impossible to be too downbeat after a season like this."
