Ward was two games from defeat before breaking Querrey five times in the final hour of the match to win in five sets and give Great Britain a 2-0 advantage in the tie, and the world number 175 has admitted that it was his biggest achievement in the sport.
Asked whether it was the greatest win of his career, the 26-year-old told BBC Sport: "It is. Sam's ranked pretty high. The one against Dmitry Tursunov [of Russia] was also a massive win for me.
"I hope to use it to push on from here. I love playing for my country and it shows in my performance."