A Donny van de Beek goal saw Ajax grab a vital away goal as they beat Spurs in the first leg, giving the Eredivisie outfit a crucial advantage to take back to Amsterdam.
However, Lucas believes that a comeback is possible if they perform the way they did in the second leg of the quarter-final, where they lost 4-3 on the night but progressed to the last four on away goals.
“Were voices raised [at half-time against Ajax]? Yes, you know Mauricio [Pochettino],” Lucas said.
“He loves to touch our minds and to motivate, he is so good at this. That’s why we changed in the second half and we played much, much better.
“That’s why we are going there to play the game otherwise we might as well stay in London, give up and let them qualify. One-nil, things can happen. A game is 90-95 minutes and a lot of things can happen.
“Look at when we played Manchester City in the second game. In 20 minutes there were five goals. Who could believe that? No-one.
“The spirit against City was amazing, was unbelievable, and we need to play like that.
“We went there and played against City and we did a very good game. We were strong mentally because it’s important. And now we need to do the same.
“Run, fight. Like I said, we can go there, I believe in my team-mates, let’s rest well now, prepare for the next game and believe always.
“Hopefully when we go there we will score a lot of goals and get the qualification. That would be amazing for us and all the Tottenham fans.”
Moussa Sissoko reiterated his team-mate's belief and insisted the team are focused on producing a better showing than they did in the first game, where they were lacklustre for the first half in particular.
“I believe we will go to Amsterdam and come back with qualification because I know the quality of this team,” he said. “I know we have a lot of character and with the first result, we are not happy. We should do better.
“So now we want to go there and come back with the win and qualification.”