But Sexton, who was overlooked for the Lions' kicking duties thanks to Halfpenny's fine form with the boot throughout the tour, refused to blame the Welshman for a heart-breaking loss.
"It was a tough ask for Leigh to hit that. It was all of 50 metres or so, so it was an extremely difficult kick. Also, it was the last kick of the game and with everything that was riding on it he had to get it right," said Sexton.
"It's small margins but you can't look at one man. There was plenty wrong with our performance as a team.It didn't come down to one kick - we need to examine how we played.
"We probably felt he could get the kick, and Leigh felt he could too. We've seen him knock them over from that kind of distance before, but it's right on his range. It was a very tough kick, and you have to also remember how tired he must have been right at the death.
"We are all pretty devastated because we know just how close we came. It's a tough one to take but if we're honest with ourselves we didn't deserve to win, it's as simple as that."
Despite his honesty after the early chance of series success slipped by at the Etihad Stadium, Sexton insists that the Lions remain confident of wrapping things up in Sydney next week.
The disappointment of defeat is still raw but Sexton and co have no intentions of giving up the ghost with a week still to go.
"It's difficult to reflect…but we are in the same position next week. We didn't take it (the chance), and we have to learn from it and get better for next week. We are in the same position again, and hopefully we can do better," added Sexton.
"We just need to look at our performance. It's hard to take, but we are going to have go back, sit down with the coaches, probably Monday and Tuesday, and bounce back.
"We were 1-0 up and we should have gone 2-0 up, and we didn't. At times it felt we were wishing the game to finish, rather than going out and going after it. That's how I felt, anyway.
"We knew it was small margins last week, and it was the same this week. It comes down to taking your chances. We had chances to score tries - tries win games - and they took their chance at the end."