Stepanek is 4-2 against Monaco, who is the highest ranked Argentine at No. 30.
Thursday's draw also pits Tomas Berdych against Leonardo Mayer. In Saturday's doubles, the Czech pair of Lukas Rosol and Jiri Vesely will face Carlos Berlocq and Horacio Zeballos.
Reverse singles are scheduled for Sunday.
The winner will face either Serbia or Canada in the final in November.
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