Raucous home support for holders Argentina did not make up for the absence of Juan Martin del Potro and Federico Delbonis on Friday (Saturday AEDT) as they fell 2-0 behind to Italy in the first round of the Davis Cup.
Croatia, runners-up last year, were without their top man Marin Cilic but managed to end the opening singles level 1-1 with a Spanish team lacking Rafa Nadal after Franko Skugor upset Pablo Carreno Busta over five sets.
Only Serbia, champions in 2010 and facing Russia at home in Nis, had the services of a top-10 player in Novak Djokovic and they took a 2-0 lead.
Djokovic, who readjusted his start to the season after a shock early exit from the Australian Open, had a scare when he dropped the first set to Daniil Medvedev but prevailed 3-6 6-4 6-1 1-0 when the young Russian retired.
Viktor Troicki had earlier beaten Karen Khachanov 6-4 6-7(7-3) 6-3 1-6 7-6(7-6).
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Del Potro, like most of tennis's leading men, had announced before the season began he would not be available for the opening round of the World Group.
This left top seeds Argentina, a British team without Andy Murray and the Swiss minus Roger Federer and Stan Wawrinka vulnerable to defeat.
Argentina won away in every round last year, but in Buenos Aires Guido Pella lost 6-3 6-3 6-3 to Paolo Lorenzi and Andreas Seppi beat Carlos Berlocq 6-1 6-2 1-6 7-6(7-6) to leave the holders on the brink of elimination.
"For the first time I felt uncomfortable playing the Davis Cup," Pella, who had last helped Argentina upset Britain in the 2016 semi-final in Glasgow, told reporters.
Germany's Alexander Zverev won his first Davis Cup point when he beat Belgian debutant Arthur de Greef 6-3 6-3 6-4 to level their tie at 1-1 in Frankfurt.
Earlier, Steve Darcis had come back from 3-0 down in the fifth set to beat Phillip Kohlschreiber 6-4 3-6 2-6 7-6(7-2) 7-6(7-5).
Britain, facing a Canada team without Milos Raonic in Ottawa, made a good start when Dan Evans beat Denis Shapalov 6-3 6-3 6-4.
Jack Sock put the United States on the front foot against Switzerland by beating Marco Chiudinelli 6-4 6-3 6-1 in the first rubber in Birmingham, Alabama.
"The court here is the polar opposite to Melbourne, it's a slow, gritty, high bouncing court. I love it," Sock said in a courtside interview having played at the Australian Open last month.
Meanwhile, Pierre-Hugues Herbert and Nicolas Mahut clinched France's first-round match against Japan in Tokyo on Saturday with a 6-3 6-4 6-4 doubles win over Yuichi Sugita and Yasutaka Uchiyama.
France will play the winner of the Great Britain-Canada tie in the quarter finals.
