Isner posted a 6-3, 6-2, 7-5 win over Gilles Simon after France's Jo-Wilfried Tsonga opened the best-of-five series with a 7-5, 6-2, 2-6, 6-2 victory over Ryan Harrison.
Isner and Tsonga are scheduled to square off in the first singles match Sunday, which will be the first opportunity for one team to secure a berth in the Davis Cup semifinals.
The United States will send out twin brothers Bob and Mike Bryan -- the No. 1 doubles team in the world -- against Frenchmen Julien Benneteau and Michael Llodra for Saturday's double match.
Simon and Harrison are paired against each other for Sunday's second singles match -- the fifth of the series.
The U.S.-French winner would go against either Austria or Spain in the semifinals Sept. 14-16. Spain is up 2-0 against Austria in their series.
Tsonga committed 53 unforced errors and lost his serve four times against Harrison. But three of the breaks were in the third set and Tsonga came back in the fourth with 21 winners in putting away the match.
Isner piled up 53 winners and fought off all five of Simon's break-point chances. Simon had a set point at 4-5 of the third set but Isner rallied to hold serve, post his fourth break of the day and serve out for the match.