Valencia gave the Athletics a lead in the first inning with his third career grand slam Friday night in the Mariners' 11-8 victory over the A's.
"It's always nice to get off to a good start, but it wasn't enough," Valencia said. "It's frustrating, but that's how it goes sometimes. It's tough when you're not winning."
Valencia has hit six of his 13 home runs since joining the A's and has been so impressive at third base, the A's moved Brett Lawrie to second to make way for Valencia.
Valencia was also Lawrie's teammate with the Blue Jays. Lawrie came to Oakland as part of a trade that sent Josh Donaldson to Toronto. Valencia, who was designated for assignment by the Blue Jays at the end of July, was practically free.
"They've been doing that for a while power-wise and with productive at-bats," A's manager Bob Melvin said.
Valencia, on a nine-game hitting streak, said he's kept the same approach all year.
"I've been playing all year, since Spring Training," he said. "We've all worked hard during the offseason to get ready."
Valencia played first base and the outfield when Donaldson arrived with the Blue Jays. While he doesn't think he needs to prove anything, he's aware some of the younger guys are auditioning.
"Guys are trying to open some eyes," he said. "A lot of jobs will open up and guys have the oppportunity to set themselves up for next year."
Valencia has already stated his case loud and clear.