Down by more than a dozen points in the Virginia governor race, Republican Ed Gillespie has surged ahead of Democrat Lt. Gov. Ralph Northam by a single percentage point, turning the sleepy little bellwether election into an overnight barn-burner.

New polling by Monmouth University shows the two men deadlocked 48 to 47 percent. And while the contest was narrowing slowly earlier, Gillespie now has the momentum with just three weeks until Election Day.

Geography explains the surge and could determine the result.

Unsurprisingly, up in liberal Northern Virginia, Northam has fortified a lead of 64 to 32 percent. Former Vice President Joe Biden stumped for the Democrat in the wealthy D.C. suburban area on Saturday. And down in conservative Western Virginia, Gillespie has amassed a mirroring lead of 64 to 31 percent. Vice President Mike Pence traveled to the crowded state fair in Abingdon on Saturday to rally for Gillespie.

And in an interesting and perhaps embarrassing twist for Northam, Gillespie has surpassed the lieutenant governor in the Democrat's backyard: Gillespie is up 48 to 45 percent in Eastern Virginia.

"As the northern and western parts of Virginia revert to their partisan norms, the battle for swing voters will occur right down the I-95 corridor," said Patrick Murray, director of the independent Monmouth University Polling Institute.

Expect both candidates to play to their policy strengths in the final stretch.

A retired physician, Northam enjoys the upper hand on both education and healthcare. As Monmouth notes, his lead in both areas has narrowed slightly but not significantly. On crime and the economy though, Gillespie hasn't just maintained his lead. He's expanded it significantly from a 35-27 percent lead in September to a 40-24 percent edge in October.

Gillespie hammered both issues during last week's debate and, according to the poll, it's working. The soft on crime narrative coupled with attacks about the sluggish economy, Murray explains, appears to be effective. "This is a game of inches right now, so any small advantage counts."

A last-minute sprint along the interstate corridor favors Gillespie, though. He always breaks late in the final stretch. In the 2014 Senate election, polls showed Gillespie down by almost 10 percentage points to incumbent Sen. Mark Warner. In the end, Gillespie lost by less than 1 percentage point.

Philip Wegmann is a commentary writer for the Washington Examiner.