The Czechs are one win away from their sixth title in eight years.
To win, the 18-time champion U.S. would have to become the first team to come back from 2-0 down in the best-of-five final at Prague's O2 Arena.
In Sunday's reverse singles, Kenin will go against Siniakova, and Riske will meet Strycova.
Siniakova broke Riske for 6-5 in the second set, but the 63rd-ranked American forced a tiebreaker. The Czech dominated it, however, converting the second match point when Riske sent a backhand wide.
The Czechs also are weakened, missing top-10 players Karolina Pliskova (injury) and Petra Kvitova (illness). Another mainstay, Lucie Safarova, announced Saturday she will retire from tennis after the Australian Open because of health problems. She has won four Fed Cups.
Playing in her last tie, the 32-year-old Strycova won her match with a backhand winner at the net on her first match point to improve to 11-7 in Fed Cup singles.
"I'm so happy that I could win today in front of such a crowd," Strycova said. "It's funny because it's her [Kenin] first one, and this is my last one, so for me it was a lot of emotions."
Strycova broke Kenin in the opening game of the decisive set to take control. The 19-year-old Kenin looked nervous and served three double faults to trail 5-2.
Both players made 32 unforced errors, and the American had 23 winners -- two more than her opponent -- but Strycova made her experience count in the decisive points.
"For my Fed Cup debut, I was pretty nervous, but I was able to handle it once I stepped on the court," Kenin said. "The atmosphere was just incredible."