They had to comeback against both Rennes and BATE Borisov to reach the final eight.
Kolasinac has warned that slow starts over the first 90 minutes need to be avoided now the competition is hotting up.
"It's really important, obviously it's always very difficult when you lose the first game," he replied when asked how key a positive result will be in the first leg next time round.
"We are aware of that, it's not something we want to do of course. It is something we are going to work on in the next round. Of course the key will be to start better than we have in these last two ties.
"We didn't put ourselves in a good position at the end of that first leg. Having said that, I think that away goal was crucial for us.
"It was difficult for us because we had to play with 10 men for about 50 minutes of that first game as well. We made it difficult, but we knew how strong we are at home and we deservedly went through tonight."