How do I fight lustful thoughts with prayer?

When I say prayer, I don't mean simply saying, God help me. That's not really enough. We need the Jesus Prayer: Lord Jesus Christ, have mercy on me. There is power in the name of Jesus Christ. At his name every knee shall bow in heaven and on earth, because Christ is God. When the provocation comes, we flip into defensive mode and keep the prayer repeating in our mind until the enticement lifts.

It is not a mantra or mindless repetition. It is a quick way to keep our mind focused on Christ. Remember Peter on the waves: when he became distracted by the wind and took his eyes off Christ, he began to sink. So when the temptation begins to form, we cut it off at the first thought, sink down into the heart, and pray: Lord Jesus Christ, have mercy on me.

We are admitting to Christ, I am tempted, and I don't want this to take any root in my heart. If we have a prayer rope, bring it out: the tangible experience of touching it keeps us focused. I knew a person who struggled intensely with lust from their youth. After several years in the church they said, Father, I can't even confess lust, because there's no lust happening in my heart.

Not that they were miraculously healed and found no one attractive. They said, I've been saying the Jesus Prayer and I haven't been letting any of it into my soul. It's there knocking on the door wanting to get in, but it isn't inside of me anymore. That is the first and most important line of defense, and it takes our voluntary participation.