Sam Querrey put the Americans ahead by beating Peter Luczak 6-7, 7-6, 6-3, but former No. 1 Hewitt outplayed 19th-ranked Isner in a 6-2, 6-4 victory to even the score.
A doubles match on Monday will decide the winner of the opening tie in the Red Group, which also includes Spain and the Czech Republic.
Story continues below ↓advertisement | your ad hereThe Blue Group is made up of Argentina, France, Germany and defending champion Serbia.
The winner of each group will meet in Saturday's final.
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