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Wimbledon champion Muguruza proved much stronger on serve than the defending champion, advancing to Sunday's final in less than 80 minutes.
The Spaniard ended a run of six consecutive defeats against Czech Pliskova.
Muguruza will play either Romanian Simona Halep or American Sloane Stephens in the final.
In the day's second match, Simona Halep qualified for the final with a victory over home favourite Sloane Stephens.
The Romanian, ranked number 2 in the world, won 6-2 6-1.
2-Simona Halep (Romania) beat Sloane Stephens (U.S.) 6-2 6-1
4-Garbine Muguruza Blanco (Spain) beat 1-Karolina Pliskova (Czech Republic) 6-3 6-2
Stage 7, Vasto - L'Aquila (185km)