The Reds' inconsistent form, including back-to-back losses to West Brom and Zenit, have given way to poor performances, but the Brazilian believes the result on Sunday was the best way to bounce back.
"We started the week thinking it could be a really good week for us," Lucas told reporters. "But we had the defeat to West Brom and then the Europa League loss, but we have finished the week off in a positive way by scoring five goals and keeping a clean sheet.
"We know we still have to improve a lot but this victory will give us confidence going into Thursday to try to get through against Zenit.
"With the way we played over there, we created a lot of chances, if we do that again and take them then we'll have a great chance of getting through to the next stage.
"But we also have to defend well on Thursday because if we concede an away goal it will be very difficult for us.
"We have to make sure we go with a positive and offensive mentality but knowing that if we concede it's going to be very hard."
The defensive midfielder, who has recently recovered from injury, believes the club can finish the season on a positive note if they can turn in consistent performances.
"It's difficult to explain. As players you get frustrated a lot of times as well," Lucas said. "When you think we are starting to get some good momentum we have a defeat and a setback.
"But there is still time to get that consistency. Our league position is not great [seventh, with nine points off the top four having played one match more] but we must keep fighting and see what happens.
"If we can get that consistency then we can finish this season on a high."