Asian champions lose 1-0 to the US, while Mexico edge out Canada in a match briefly stopped due to homophobic chants.
Zardes replaced Daryl Dike in the 63rd minute and combined with two other second-half subs, Nicholas Gioacchini and Eryk Williamson, to score his 14th international goal and second of the tournament on Thursday.
CONCACAF filled out the field for the Gold Cup, the championship of North and Central America and the Caribbean, with the 2022 World Cup hosts Qatar as invited guests.
Qatar had a chance to go ahead in the 61st minute but Hassan al-Haydos sent a penalty kick over the crossbar following a foul by James Sands.
Meanwhile, Hector Herrera scored in the ninth minute of second-half stoppage time to give Mexico a dramatic win over Canada in a match briefly stopped in the second half due to homophobic chants.
Orbelin Pineda converted a penalty kick in the second minute of first-half stoppage time to put Mexico ahead before Tajon Buchanan equalised in the 57th minute, the first goal conceded by Mexico in the tournament.
The referee halted play in the 86th minute after Mexican fans were heard shouting a homophobic slur.
In the ninth minute of injury time, Herrera took a pass from Rodolfo Pizarro and slotted a shot from 16 yards to seal his side’s progress.