The injured third baseman was in Pennsylvania to play rehab games with the minor league Scranton/Wilkes-Barre Yankees.
A-Rod showed up at the casino at about 8 p.m., workers told The Post.
He had a steak dinner and then entered a special high-roller gaming room with two pals, according to workers.
"There are mostly slots and blackjack tables in the high limits room," the blackjack dealer said, noting that the room is often set up with a special table for big-time gamers to play poker.
Another card dealer at the Wilkes-Barre, Pa., casino saw the Yanks slugger enter the high-stakes room.
Star-struck Poconos gamblers tried to chat A-Rod up as he passed through the casino, but witnesses said he and his pals did not want to be hassled by patrons.
"I saw a few women approach his entourage to get a picture with him but they were turned down and told to 'Keep walking.' It was sad seeing that," she said.
A greeter in the high-limit room saw A-Rod enter and estimated he was there for about two hours.
"They wanted to keep to themselves," the greeter said.
The evening started with dinner at the casino's Ruth's Chris steakhouse.