Australia's narrow win last weekend levelled the series at 1-1 heading into the final Test in Sydney, with the Lions aiming for their first series win since beating South Africa in 1997.
Roberts, who has been named alongside fellow Welshman Jonathan Davies in centre, believes that he has a duty to perform in what he considers one of the biggest matches in world rugby.
"Bar maybe a World Cup final, I doubt there is a bigger game in rugby for us boys. You just have to get completely excited about it, not shy away from it, not get nervous. It's just pure excitement, go out and express yourself, keep your concentration and deliver under pressure," said Roberts.
"I see it as a responsibility. I've been picked to do a job and it is important I deliver. I've always thought that I thrive under pressure in big games, it's where I like to play. The higher the pressure, the more responsibility is put on me, the more I thrive and the more I enjoy it.
"I am on my second tour now, and I think any player who is on their second or third tour who has played quite a bit of international rugby, you have to take responsibility. That is something I enjoy and thrive on. I see myself as one of those guys who has to lead the way. It will be big mind games on Saturday, a huge mental challenge as well as a physical one. It is about staying completely focused."