The No.2 seed needed just an hour and 26 minutes to defeat Siegemund in straight sets, 6-3 6-3.
Pliskova actually fell to a 1-3 deficit early in the first set, but the big-hitting Czech reeled off five consecutive games to claim the first set in 44 minutes.
The second set saw Siegemund struggle with consistency in the fourth game, eventually dropping serve and giving her opponent a 3-1 lead. Pliskova never looked back, consolidating the break and taking the set and match.
Perhaps the most consistent player on the WTA circuit over the last two years, the Czech has yet to breakthrough and win her first Grand Slam. The recent Brisbane champion employs a huge serve with powerful groundstrokes, and is always considered a threat to the top-ranked players. She plays the winner between Taylor Townsend and Anastasia Pavlyuchenkova.
Kazakhstan's Zarina Diyas fought from a set down to defeat Russian youngster Anna Blinkova 4-6 6-3 6-4, while Catherine Bellis upset Karolina Muchova 6-4 6-4.
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