Mark Watson's men piled on four second-half goals at the Buck Shaw Stadium in California, as they ended a six-match winless run in emphatic fashion.
Shea Salinas opened the scoring for the Earthquakes just prior to half-time, collecting the ball on the left sideline before weaving his way into the area and unleashing a powerful strike into the top-right corner.
Atiba Harris doubled San Jose's advantage seven minutes after the interval, cleaning up the scraps from Chicago goalkeeper Sean Johnson's save from Chris Wondolowski's strike.
Wondolowski made amends and got on the scoresheet, making it 3-0 in the 62nd minute.
Fire's Grant Ward scored his first goal for the franchise, with a one-touch effort from outside the area in the 75th minute.
However, it would prove consolation - as Yannick Djalo and Cordell Cato added the Earthquakes' fourth and fifth goals respectively as they chalked up their fifth win from 18 league games.
San Jose remain rooted to the foot of the Western Conference, three points behind second-bottom Chivas USA but with a game in hand.
The Fire are eighth in the Eastern Conference on 20 points, only four behind the fourth-placed New York Red Bulls.