In for a penny, in for . . . $3.5 million.

The luckiest gambler on the planet dropped a penny in a one-cent “Wheel of Fortune” slot machine at Atlantic City’s Borgata Hotel on Sunday — and came away a millionaire more than three times over, the casino said yesterday.

It was one of the highest penny-slot payouts since legal gambling came to the Jersey Shore resort town in 1978, according to a Borgata official.

And that wasn’t the only big win of the day.

Another gambler, playing a few hours later, sprung for 50 cents on another “Wheel of Fortune” machine — and walked away with an extra $700,000 in his pocket.

Both winners are from New York and asked that their names not be released.