Yost is referring to the trade that sent Cespedes, a promising outfielder with the Athletics, to the Red Sox for Lester and outfielder Jonny Gomes.
By the end of the day, the Boston-Oakland blockbuster was overshadowed by an American League Central division rival's big splash.
The Tigers acquired Rays starter David Price in a three-way trade just before the non-waiver Trade Deadline passed.
"It was a nice acquisition. It's a nice pitcher to have, but that doesn't change what we're trying to do," Yost said. "Is it going to make it tougher when we face [Detroit]? Yeah, I mean, that's a pretty good rotation over there, but we like our rotation too."
Jackson Alexander is an associate reporter for MLB.com.