The "underage" animal attempted to slip into the downtown Reno venue ahead of the breakfast rush, according to The AP.
Nevada Department of Wildlife spokesman Chris Healy said the male cat's behaviour was "almost the equivalent of being a stupid teenager".
He added that coming-of-age cougars often end up in inappropriate locations after being chased out of a territory by adults.
Guests at Harrah's spotted the mountain lion trying to walk into the casino on Friday morning. He struggled to work the revolving door and took refuge under an outdoor stage in a nearby plaza.
State wildlife officials tranquilised the 2-year-old animal and plan to release it back into the wild after tagging it for participation in a University of Nevada, Reno study.
No injuries were reported following the incident.
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