The 29-year-old swept Kyle Edmund, Dominic Thiem, David Goffin and Nadal en route to his second ever ATP 500 title.
Querrey, who is no stranger to tennis shocks, admits his belief just kept growing stronger as he powered through the week.
“This game is all about confidence, and I think I found it this week,” said the American.
“I was really focused on being aggressive. I'll remember this for the rest of my life. Beating these players here gives me a ton of belief that I can do it more often.”
Few expected the 29-year-old to be pitting his wits in Saturday’s final at the start of the week but Querrey’s brand of tennis, heavily reliant on the forehand, suited to the court conditions in Mexico.
“I'd get a short ball and rip it down the line or go crosscourt more than I usually do,” he added.
So much so that Querrey broke serve 17 times throughout the tournament and dropped only a single set to the top 20 players he defeated.
Querrey entered the tournament in Mexico on the back of a quarterfinal showing at Delray Beach but his form over the last six month has wavered dramatically.
The 29-year-old famously dumped the hitherto imperious Novak Djokovic out of Wimbledon last summer but has failed to capitalize on that remarkable feat.
However, the American’s triumph in Acapulco will see his ranking improve by 14 places – from 40 to 26 – and make him the third-ranked American on the singles tour, hanging on the coat tails of John Isner and Jack Sock.