In the past?

[tkorbitz]

What is the correct form of the verb when saying, "I was winning" in Spanish? How do I say that?

[hermit]

The precise form will depend on context, but for starters, how about
"(Yo) estaba ganando...?

[tacuba]

To add to Hermit's suggestion, you could also use "ganaba" when referring to an unspecified time and duration in the past.

"When I lived in Las Vegas I was winning all of the time."

[CrOtALiTo]

What is the correct form of the verb when saying, "I was winning" in Spanish? How do I say that?

The correct way to say it into of the Spanish is Estaba ganando.

I hope that my contribution can help you