Alcaraz was "really, really solid," in his assessment, against Giulio Zeppieri, while Swiatek topped Rebecca Sramkova.

They will face Slovakia, which followed up its upset of the U.S. with a win over Australia. Italy and Poland will play in the other semifinal.

Viktoria Hruncakova and Tereza Mihalikova completed the surprise victory, surviving a late rally by Taylor Townsend and Ashlyn Krueger.