Rob McMillan (72) and Jon Turcott (66) shared third place at minus-9. Paul Danielson carded a 1-under 71 and finished in solo fifth at 8-under-par 280.
Johnson made his move up the leaderboard when he holed out for eagle from 125 yards out at the par-4 sixth. Quiroz fought back on the second nine but missed a 2-footer for par at the 15th.
Johnson birdied the same hole and it was off to the winner's circle.
'I feel very good right now,' said Johnson, who became the fifth consecutive American to win on the Canadian Tour. 'Guadalajara is a great city, and this course is beautiful. Alex sure made it exciting in the end.'
For Quiroz, a three-time Mexican amateur champion, he will have to wait until next week for a shot at win No. 1.
'The putt I missed on 15 did it,' said Quiroz. 'I never thought I would miss it. I am a little frustrated right now, but I'll get over it.'
The win was Johnson's third on the Canadian Tour. Last year he won the TravelTex.com Canadian Tour Challenge and the Edmonton Open for his first victories on tour.
Jason Higton (68), Kris Mikkelsen (72) and Matt Weibring (72) shared sixth place at 7-under-par 281.
Anders Hultman (70), Jeff McCammon (72), Rob Oppenheim (75), Antonio Serna (70) and Stephen Woodard (72) tied for ninth place. That group came in at 6-under-par 282.