World tennis number one Rafa Nadal's return helped Spain make a commanding start in their quest to regain the Davis Cup but Novak Djokovic's absence left holders Serbia surprisingly struggling against India.
Australian Open champion Djokovic, the best player in the world on current form, skipped his country's World Group first round tie against India to prepare for Indian Wells next week.
However, that decision could return to haunt Serbia who ended the first day locked at 1-1 in Novi Sad.
Spain roared into a 2-0 opening day lead against Belgium in Charleroi despite a late reshuffle in which Fernando Verdasco replaced the injured David Ferrer.
The United States and Chile, possible quarter-final opponents for Spain, were all square after the first day in Santiago.
Germany and Croatia were tied at 1-1 in Zagreb while World Group debutants Kazakhstan shared the opening day's singles with the Czech Republic in Ostrava.
Former US Open semi-finalist Joachim Johansson, now ranked 749 in the world after terrible injury problems, helped Sweden take a 2-0 lead against a below-strength Russia in Boras.
Argentina were 2-0 to the good against Romania, although David Nalbandian is a doubt for the rest of the tie after injuring himself in a victory over Adrian Ungur.
France also led 2-0 against Austria inside an aircraft hangar at Vienna's international airport.
