Wawrinka, who has already won three titles this year including his second grand slam in Paris, needed just 50 minutes to defeat Krajicek .
The Swiss will play Luxembourg's Gilles Muller on Saturday after he upset French third seed Gilles Simon 6-3 6-4 in the quarter-finals.
Kei Nishikori fought back to beat Marin Cilic 3-6 7-5 6-3 to record his second successive win against the player who beat him in last year's U.S. Open final.
Nishikori, who won his home tournament in 2012 and 2014, set up a showdown with Frenchman Benoit Paire for a place in Sunday's final.
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Paire also from behind to defeat Australia's Nick Kyrgios 3-6 6-4 6-1.
(Writing by Julian Linden in Singapore, editing by Pritha Sarkar)
