Teenager Melanie Oudin beat Julie Coin to give the Americans an unassailable lead at France on the way to a 4-1 victory, while Francesca Schiavone rallied from a set down to beat Kateryna Bondarenko and help Italy to a resounding 4-1 win against Ukraine.
The Czech Republic reached a second consecutive Fed Cup semifinal by beating Germany in the decisive doubles match.
It also went down to the doubles as four-time champion Russia defeated Serbia 3-2 as Svetlana Kuznetsova and Alisa Kleybanova beat Jelena Jankovic and Ana Ivanovic 6-1, 6-4 in the decisive rubber.
Earlier Sunday in the reverse singles, Kleybanova beat Ivanovic 6-2, 6-3 while Jankovic defeated Kuznetsova 6-3, 4-6, 6-3 to level the tie.
Russia, which has won four of the last six Fed Cup titles, will now meet the United States, who trounced France 4-1, in the semifinals.
Oudin defeated Coin 7-6 (3), 6-4 on the indoor clay court at the Stade Couvert Regional de Lievin in just over two hours in the first reverse singles.
The 18-year-old Oudin broke Coin in the fifth game of the second set and clinched the match when the Frenchwoman shanked a forehand.
Oudin had saved two break points at 5-5 in the first to force the tiebreaker, where she hit three straight winners to close out the set.
"I was a little nervous in the beginning," Oudin said. "She definitely stepped up her game when she came out on court and served some really great service games.
"There wasn't much I could do in the beginning, besides staying in there with her."
Alize Cornet had been scheduled to face Oudin but France captain Nicolas Escude decided to replace her with Coin after Cornet acknowledged she struggled with her nerves against Bethanie Mattek-Sands in the opening singles Saturday.
With the U.S. through, France restored some pride with Pauline Parmentier's 6-4, 6-4 win over Christina McHale before Mattek-Sands teamed with Liezel Huber for a 6-2, 6-3 doubles win over Cornet and Stephanie Cohen-Aloro.
Both teams were missing their best players. Serena and Venus Williams skipped the event, while France played without Marion Bartoli, Aravane Rezai and Virginie Razzano.
The U.S. improved its record against France to 11-1 in Fed Cup play and will next face Russia on April 24-25.
Ivanovic, the former No. 1 who has dropped to 23rd in the WTA rankings after a string of poor results since winning the French Open in 2008, struggled on her serve against the 31st-ranked Kleybanova and committed 51 unforced errors.
"I tried to play more aggressively, but I'm struggling psychologically," a teary-eyed Ivanovic said.
Italy and Ukraine started Sunday at 1-1 in Kharkiv before Flavia Pennetta beat Alona Bondarenko 7-5, 7-6 (3) to put Italy ahead.
Both players struggled with their serve in that match, which featured nine breaks, but Pennetta proved stronger at the end of each set.
Bondarenko held a 4-2 lead in the first set and had a break point for 5-3 before Pennetta rallied, and the Italian then dominated the second-set tiebreaker to clinch the win.
Schiavone then struggled in the first set and was broken twice before racing out to a 5-0 lead in both the second and third.
Roberta Vinci and Sara Errani beat Mariya Koryttseva and Viktoria Kutuzova 6-1, 6-3 to complete the win.
Italy will play the Czech Republic after Lucie Hradecka teamed up with veteran doubles specialist Kveta Peschke to defeat Anna-Lena Groenefeld and Tatjana Malek 6-1, 6-3 on indoor hardcourt at the Brno Exhibition Center.
Italy beat the Czechs 3-2 in their last Fed Cup encounter in 2005.
"Hopefully we'll beat Italy this time," Peschke said. "It will be revenge."
The Czech pair dominated the first set before the Germans got briefly back in the match with a 2-0 lead in the second. The Czechs finally converted the sixth break point in the sixth game and went on to secure a comfortable victory.
Earlier Sunday, Groenefeld rallied to overcome Petra Kvitova 4-6, 6-3, 6-2 to draw Germany even at 2-2 after Hradecka beat Andrea Petkovic 6-1, 7-6 (5) in the first reverse singles to give the Czechs a 2-1 lead in the series.
Kvitova had rallied from 2-0 down in the first set but struggled the rest of the way and lost in a little over two hours.
"I didn't serve well," Kvitova said. "That was the biggest problem."
In World Group II, Australia beat Spain 3-2 in Adelaide, Belgium beat Poland 3-2, Estonia beat Argentina 4-1 and Slovakia beat China 3-2.