Robertson reflected in Liverpool's performance after the game, saying: "We didn't start great, we gave away too many cheap balls, we went quiet in the game.
"It took us a wee while to get going, which at this level we can't do. In the first half we got punished for it."
He added: "The goals were cheap from our point of view and then you find yourself 2-0 down.
"We weren't at the races but the only positive is we got an away goal. Lets see if that will be crucial or not. But next week we need to play a lot better than we did this week.
"Our reaction was good. The back-end of the second half we were ok and the second half we were good."
Robertson also admitted: "We got the goal through Mo and like you said, 2-1 you're right in the tie and right in the game. It's just disappointing the lose the next one.
"Then the last 10-15 minutes we couldn't really get close to them. They were really good at keeping the ball and killing the game.
"They've got so many experienced players like Modric and they can do that so easily. Unfortunately we just couldn't get near the ball to get any more chances going up the other end."