Which ship, part of a Spanish fleet to colonize the Spice Islands in the East Indies, reached the Pacific coast of Mexico in July 1526, achieving the first navigation from Europe to the western coast of North America?

Not sure if the question is asking about a direct route, at the time I don't believe any ship could make it from Europe to the Pacific without stops along the way... However Ferdinand Magellan sailed into the Pacific via what's now known as the Strait of Magellan in 1520 with three ships (Trinidad, Concepción, and Victoria). He started out from Seville, Spain and eventually reached the The Philippines.

King Charles I funded Magellan and he set sail September 20, 1519 with a fleet of five ships and roughly 200 men. The five ships were: the Trinidad, captained by Magellan; San Antonio, captained by Juan de Cartagena; Concepción, captained by Gaspar de Quesada; Victoria, captained by Luis de Mendoza; and the Santiago, captained by Juan Serrano.

on October 21, 1520 he finally found the passage they were searching for. Shortly after entering the passage, the San Antonio deserted the mission. On November 8, 1520 the Trinidad, Concepción, and Victoria reached the "Sea of the South." Today we know it as the Pacific Ocean. This passage at the tip of South America that Ferdinand Magellan had found would later be renamed the Strait of Magellan.

Ferdinand Magellan had problems along the way, but he had finally reached the Pacific Ocean. Once through the strait, Magellan continued northward up the coast of Chile. In March the reached the island we now know as Guam. Here, they found and ate fresh food for the first time in 99 days.

https://exploration.marinersmuseum.org/subject/ferdinand-magellan/

Garcia Jofre de Loaisa led an expedition, planning to establish a Spanish colony in the Spice Islands, that left Spain in 1525, and after travelling through the Straits of Magellan travelled up the west coast of South America, ultimately reaching Mexico in July 1526. The voyage was not terribly successful - only one ship made it to the Spice Islands, and they returned to Spain in 1536.

https://en.wikipedia.org/wiki/Loa%C3%ADsa_expedition