In 2002, Zach qualified for the BellSouth Classic while traveling back from an NGA Hooters tournament. He finished the event in a tie for 17th place. Two years later as a PGA TOUR rookie, Zach won the BellSouth Classic for his first career PGA TOUR victory.

Johnson's wife, Kim, had manufactured a personal ball mark for him. On one side she inscribed the words, "Trust your line," accompanied by the notation Proverbs 3:5,6, which says: "Trust in the Lord with all your heart, and lean not on your own understanding. In all your ways acknowledge Him, and He will make your paths straight." Johnson would set that side up on the putting green and recite the proverbial words to himself. The reverse side of the homemade mark helped shape Johnson's mindset elsewhere on the course. The inscription was, "One shot at a time," and the Scripture passage was Matthew 6:33-34: "Seek first the kingdom of God and His righteousness and all these things will be given to you. Do not worry about tomorrow, for tomorrow has enough worry of its own." "Those verses kind of kept me at ease," Johnson says. "I don't know if I was communicating with God at the time I was playing, but I felt like I was closer with Him at the time than with anybody else."

According to the PGA website, Johnson won the final three regular-season events on Hooters Tour in 2001, "earning the nickname 'Back-to-Back-to-Back-Zach'".

In 2003, Zach played on the Nationwide Tour, winning twice (Rheem Classic, Envirocare Utah Classic). Zach topped the money list on the Nationwide Tour with record earnings. By placing in the top 20 on the year end money list, Zach automatically qualified for the 2004 PGA Tour.

In 2007, Zach won his third PGA Tour Event, The AT&T Classic (formerly The Bellsouth Classic).

In both 2001 and 2002, Zach won the Iowa Open Golf Tournament.