The robbery comes two months after $1.5 million in chips was stolen during an early-morning stickup at the nearby Bellagio hotel-casino. In that case, the robber parked his motorcycle outside, walked in wearing a helmet, robbed a craps, ran out and rode away. The suspect, Anthony Carleo, 29, was arrested earlier this month.
A casino official familiar with the facts of Thursday's robbery described the robber and said he made off with about $21,000 in $1,000 chips. The rest of the chips stolen were worth $500, $100 and $25 each. The official requested anonymity because he was not authorized to publicly release details about the crime.
The Rio is owned by Caesars Entertainment, the world's largest gambling company by revenue, and is home to the annual World Series of Poker.
The man began grabbing chips from a table game when a dealer slapped his hand away, Martin said. That's when the burglar produced a gun, he said.
The casino remains open.
Charges against him include armed robbery and assault. Carleo appeared in a Las Vegas court on Wednesday during a preliminary hearing in which a judge set bail at $1 million. Jail records showed Carleo still in custody on Thursday morning.
The Bellagio robbery was different from the Rio holdup in that most of the chips stolen were worth $25,000 each -- a denomination unusual for most gamblers. Chips worth $1,000 each or less are far more common in Sin City casinos, making them far tougher to track individually.