World number one Rafael 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 on Friday.
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.
After Viktor Troicki scraped past Rohan Bopanna, a player 600 rungs below him on the tennis ladder, 6-3, 6-3, 5-7, 3-6, 6-3 India hit back when their highest-ranked player Somdev Devvarman stunned Janko Tipsarevic 7-5, 7-5, 7-6.
Saturday's doubles, when Nenad Zimonjic and Ilija Bozoljac take on Devvarman and Bopanna, looks set to be a nervy affair for the hosts who claimed their first Davis Cup triumph against France in Belgrade just three months ago.
"We definitely believe now we can win this tie and we will go out there to give it our best shot," the 93rd ranked Devvarman told reporters inside the Spens Sports Centre.
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.
For most nations an injury to a player ranked sixth in the world would be a major blow but with Nadal in the ranks and Verdasco, the world number nine, as back-up Spain captain Albert Costa has one of the easiest jobs going.
Verdasco thumped Xavier Malisse 6-4, 6-3, 6-1 before Nadal, back in action for the first time since injuring himself in a quarter-final defeat by Ferrer at the Australian Open, flexed his muscles during a 6-2, 6-4, 6-2 battering of Ruben Bemelmans.
The home crowd were offered little encouragement by their own players but at least they got to see some explosive hitting from Nadal who looked fresh and eager after his lay-off.
With Indian Wells and Miami on the horizon the French Open, Wimbledon and US Open champion was satisfied with his form in a smooth two-hour workout.
"I felt comfortable and I think that in general it was a pretty controlled match throughout," Nadal said.
"I thought I started well without making any errors. Then in the second set and at the start of the third I took my foot off the gas a bit but finished a little better."
Spain, champions in 2000, 2004, 2008 and 2009, should wrap up the tie in Saturday's doubles, rendering Sunday's singles meaningless, but several of the other World Group first round ties look set to go the distance.
The United States and Chile, possible quarter-final opponents for Spain, were all square after the first day in Santiago.
Andy Roddick beat Nicolas Massu in four sets but John Isner squandered a two-set lead against 165th-ranked Paul Capdeville, losing a gruelling match 6-7, 6-7, 7-6, 7-6, 6-4.
US coach Jim Courier will not be hitting the panic button, however, with Bob and Mike Bryan, the world's top doubles pair, in action at the Estadio Nacional on Saturday.
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.
He beat Teymuraz Gabashvili 6-3, 7-6, 6-4 after world number four Robin Soderling crushed Igor Andreev.
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.