Keys began the 12 months in excellent style, beating two-time defending champion Aryna Sabalenka in Melbourne to win a primary Grand Slam title.
However after reaching the quarter-finals of the French Open, the 30-year-old suffered a shock third-round Wimbledon exit to 37-year-old Laura Siegemund.
In New York, Keys made 37 unforced errors within the first set alone however managed to take it on a tie-break after Zarazua spurned 5 set factors.
The match appeared there for the taking for Keys as she breezed to a 3-0 lead within the subsequent set, however the 2017 runner-up in New York then misplaced 4 video games in a row.
She managed to take the set to a tie-break however double faults and errors helped Zarazua drive a decider.
Keys’ coach and husband Bjorn Fratangelo provided recommendation and encouragement all through – at one level saying: “It is only a sport, nothing’s driving on the road” – however the American’s play remained erratic.
“I wish to win, however [I was] simply feeling like successful issues means an excessive amount of. I simply could not fairly separate myself from that,” Keys added.
“When you begin enjoying badly, it simply form of all snowballs.
“I felt like I used to be simply sluggish, I wasn’t seeing issues the best way that I needed to, which I really feel like resulted in plenty of dangerous selections and lazy footwork.”
Zarazua secured her first victory towards a top-10 participant when Keys netted on match level, sparking wild celebrations among the many Mexican’s help crew after a contest lasting three hours and 10 minutes.