LAS VEGAS — For all the millions of dollars spent on this election, the outcome may come down to people like Megan Blas.

A 25-year-old college student who grew up in Guam, Ms. Blas spends up to 32 hours each week knocking on doors, canvassing voters and logging responses. There are hundreds like her in Nevada, which is serving as a fierce proxy fight for the ground war between outside groups supporting Democrats and Republicans. They are using advanced analytics and old-fashioned legwork to meet the most basic of election objectives: turning out the vote.

For years, outside groups have been building political organizations that target voters in highly refined segments, then make a final push to get their supporters to the polls, in many cases supplanting the role once played by political parties. It has become as much science as art, with mass accumulations of data. But in the final weeks, it is human contact from people like Ms. Blas that can make the difference in a close election like the Senate race here.

Ms. Blas works for a Democratic-aligned “super PAC,” For Our Future, reaching out to Asian-Americans and Pacific Islanders scattered across Las Vegas. One afternoon last week, she hopped out of a charcoal-gray Mazda and headed up the sidewalk past rows of identical tile-roofed condominiums, looking for the solitary dot on her cellphone map that identified a potential voter’s name, age and gender.