The Wallabies' woeful set-piece resulted in their 41-16 defeat in the series decider at ANZ Stadium with Alexander proving the weak link.
The 28-year-old was routed by Alex Corbisiero to the extent he was sin-binned after just 24 minutes and then failed to return to the pitch as Australia sought to escape more damage.
"After that third game I was devastated," Alexander said.
"I was looking forward to that series for such a long time. To lose the series the way we did, especially after the first two games were so close and well fought, hurts.
"For all the hype around the third game and for us to implode the way we did was just disappointing. I think the pressure got to us.
"We were like deer in the headlights with the way we played that third Test."
Corbisiero has been ruled out of Saturday's Cook Cup clash with England because of a knee injury, leaving Alexander to lock horns with Mako Vunipola in a duel that will be far more to his liking.
The second Test in Melbourne saw Alexander win that battle - Vunipola started instead of the injured Corbisiero - but he admits he will always be scarred by the outcome of the series.
"That arena has gone now and we'll never have the chance to beat the Lions," Alexander said.
"You just have to use it as fuel for the fire the next time there's a big occasion. You use that disappointment to train harder and prepare better."
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- Alex Corbisiero