John Getter / NBC News Gerardo Gamboa, a Las Vegas taxi driver, returned $300,000 to a passenger.

A big-time card shark has an honest cabbie to thank for the return of $300,000 he left in a Las Vegas taxi.

The man — whom Las Vegas police wouldn't identify other than to describe him as a well-known poker player — left the money behind in a brown case when Gerardo Gamboa dropped him off Monday morning at the $500-a-night Palms Place hotel and spa.

Cabdriver Gerardo Gamboa tells NBC station KSNV of Las Vegas that he had no interest in making off with any of the $300,000 a mysterious gambler left behind in his cab Monday,

Gamboa — who's driven Yellow Checker Star cabs in Vegas for 13 years — immediately called his dispatcher and asked his next passenger to witness that he hadn't taken anything, he told NBC station KSNV on Tuesday.

"Why? Because it [doesn't] belong to me," the honest driver said. "I just want to do the right thing."

When the doorman at Gamboa's next stop alerted him to the bag, Gamboa opened it up and pulled out a wad of about $50,000 in cash.

"It's all hundred-dollar bills. I said: 'Oh, my God! That's a lot of money in here!'" he said. "So I put back the money, and I called dispatch right away."

Gamboa said he knew nothing about his mystery passenger, other than that when they arrived at the Palms Place, "he paid me $20 for a $9.90 trip and he asked for $5 change, so [it was] a $5 tip."

"I appreciated that," he said. "That's 50 percent."

As for the stash of cash he turned in, he said he'd never seen that much money before in his life — "in a movie only."

The taxi company immediately named Gamboa its Driver of the Year and rewarded him with $1,000 and dinner for two at a pricey restaurant, The Las Vegas Sun reported.