On Saturday, Barbora Strycova, the world number 33, came from a set down against Kenin to win 6-7 (5/7), 6-1, 6-4 in the Czech's last Fed Cup rubber before retirement.
Their opening day victories ensured the Czech team will take a 2-0 lead into Sunday as they seek a sixth Fed Cup triumph since 2011 against the only the country to have won more titles.
The Czechoslovakia team that won five Fed Cup titles was 2-6 against the U.S.
But, propelled by the sold-out O2 Arena, 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.
In a hard-fought match at the O2 Arena, the 22-year-old Siniakova saved two match points when Kenin was serving at 5-4, and went on to convert her second match point on the indoor hardcourt in front of 14,500 fans.
An eventful opener set the tone as the two players combined for seven breaks of serve, Siniakova finally taking it in the 12th game on her third set-point opportunity.
"For me, it was a lot of emotions". "It's amusing because it's her (Kenin) first one, and this is my last one, so for me it was a lot of emotions". I'm extremely happy that I won.More news: Kate Upton Welcomes a Baby Girl, and Her Name Is So Precious
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Kenin admitted she was "a little bit overwhelmed" by her debut. "But I fought my hardest and I did everything I could". "I was just enjoying the moment and trying to play my game", Siniakova said.
Having survived the double scare on her own serve, Siniakova broke in the next.
"It was terrible, the worst (moment)", Siniakova said about the match points she faced.
"Actually, after the first point I was thinking, you know, you've played so many tie-breaks this year and you won nearly all".
"It couldn't be better but it isn't finished yet so we need to be ready for tomorrow".
The US, eyeing a record-extending 19th title, are missing Sloane Stephens, Serena Williams and Madison Keys.
The reverse singles, for which Kvitova could be drafted in if well enough, take place on Sunday, ahead of the final doubles rubber between world number one pair Siniakova and Barbora Krejcikova and Melichar and Collins.
But the teams may change and if Kvitova gets better, she might appear on the court.