Petra Kvitova was also out for the Czech Republic because of an illness but could play on Sunday.
The Czechs won the Fed Cup in five of the previous seven years, and Kvitova contributed to each one to sit fourth among women with the most Fed Cup trophies.
Kvitova has been troubled by high temerature after competing at the WTA Finals in Singapore and did not train this week.
In Sunday's reverse singles, Kenin will go up against Siniakova and Riske will meet Strycova. Should she play, and her team win the title, it would take her to joint third in the overall list of titles won, equalling Rosie Casals' six, and behind only Chris Evert and Billie Jean King. "I'm feeling a bit better".
Kvitova returned to the team this year after recovering from injuries she suffered during a knife attack at her home in December 2016.
But, propelled by the sold-out O2 Arena with 14,500 fans, the four-time Fed Cup victor regained composure in the second to sweep aside the Russian-born Kenin, who is still in search of her maiden WTA singles title. It will be an interesting match, ' Czech captain Petr Pala said after training, according to the CTK news agency. "I couldn't be more proud", said USA captain Kathy Rinaldi, fighting tears at a press conference. "I'm still very confident about my team". "We didn't get the result that we wanted but nobody can say that we didn't leave all out there".More news: Manchester United duo set for January exit
More news: Stunning Liverpool player returns to training in time for Red Star clash
More news: Deepika Padukone and Ranveer Singh to wear Sabyasachi for their wedding
The US are the most successful team in Fed Cup history with 18 titles so far, ahead of the Czechs who have won 10 including five as the former Czechoslovakia.
Alison Riske of the US.
Sofia Kenin of the US. "I'm looking forward to it". "It's a once-in-a-lifetime opportunity".
· No1 ranking: These two nations are current Nos 1 and 2 in the ranks, and the Czechs will stay at the top if they win.
"I hope I can use this experience", said the 22-year-old Siniakova. "We've had a great week of practice, and the pressure is on them".
"I was just trying to focus on every point (in the tie-break)", said Siniakova. "It was a long match, a lot of effort, long points, we fought hard until the end", said Kenin.