The Lions scraped victory in Saturday's opening Test, but with two left to play Sexton said that the focus must remain on improving for the next clash.
"In many ways it felt like it was gone when the penalty was given, and obviously we got a bit of luck with Kurtley [Beale] slipping," PA Sport quotes Sexton as saying.
"If it was the second Test, I am sure there would be massive celebrations, but the way we won it and it is only the first Test, there weren't big celebrations. We know there is one more to go until we do something that will be remembered."
The next Test takes place on June 29.