The Americans improved to 2-0 after beating Great Britain a day earlier. Sitting in first place in Group D with one match remaining, they are more than likely a lock to reach the knockout stage. Great Britain faces the Netherlands (1-0) on Friday.
The group stage is taking place from Tuesday through Sunday in four cities across Europe. The top two teams in each round-robin group will advance to the knockout stage in Malaga, Spain, between November 22nd-27th.
Paul swept Mikhail Kukushkin 6-1, 6-4, and Fritz took down Alexander Bublik 7-6 (6), 1-6, 6-3. Kazakhstan won the doubles match, however, with Bublik and Aleksandr Nedovyesov defeating Rajeev Ram and Jack Sock 6-2, 7-6 (6).
In Group A, Croatia earned its first win of the stage by defeating Sweden 2-1 in Bologna, Italy.
Sweden's Elias Ymer defeated Borna Gojo 6-2, 7-6 (2), but Croatia's Borna Coric responded by beating Mikael Ymer 6-4, 3-6, 6-3. It came down to the doubles match, where Nikola Mektic and Mate Pavic beat the Ymer brothers 7-5, 6-3.
Croatia and Sweden are now both 1-1. Italy (1-0) will face Argentina (0-1) on Friday.
Serbia also got into the win column in Group B by beating South Korea 2-1 in Valencia, Spain.
Dusan Lajovic beat Seong-chan Hong 6-4, 6-0 and Miomir Kecmanovic took down Soonwoo Kwon 6-3, 6-4 to secure the result. In doubles, the Koreans avoided a shutout when Ji Sung Nam and Min-Kyu Song overpowered Nikola Cacic and Filip Krajinovic 6-4, 6-2.
Serbia improved to 1-1 while South Korea fell to 0-2. Friday's match pits Spain against Canada, with both sides entering 1-0.
Australia moved to 2-0 in Group C by rallying to beat France 2-1 in Hamburg, Germany.
Their match also came down to doubles after Frenchman Richard Gasquet beat Jason Kubler 6-2, 6-4 and Australia's Alex de Minaur responded by beating Benjamin Bonzi 6-3, 1-6, 6-4. Matthew Ebden and Max Purcell were the heroes for Australia, winning 6-4, 6-4, over Nicolas Mahut and Arthur Rinderknech in just 82 minutes.
Germany (1-0) will face Belgium (0-1) Friday.