Paris: Novak Djokovic survived an injury scare and battled back from a set and a break down to help Serbia take a 2-0 lead over Russia in the Davis Cup World Group tie on Friday.
Twelve-time major winner Djokovic, just one of two of the world's top 15 playing in the first round this weekend, dropped the first set and was 0-3 down in the second against promising 20-year-old Daniil Medvedev in Nis.
Djokovic, looking to rebuild his confidence after a shock second round exit at the Australian Open, needed first-set treatment on his right shoulder before recovering for a 3-6, 6-4, 6-1 lead.
Medvedev dropped the opening game of the fourth set and then retired with cramps.
Earlier, world number 37 Viktor Troicki had given 2010 champions Serbia a winning start, downing 52nd-ranked Karen Khachanov 6-4, 6-7 (3/7), 6-3, 1-6, 7-6 (8/6) in a 4hr 30min marathon.
"The pain I had prevented me from playing the points as I wanted to," said Djokovic. "But it's a good victory and we are in a very good position."
The winners of the tie will face either five-time champions Spain or Croatia in the quarter-finals.
Despite missing former US Open champion Marin Cilic, the Croats took the lead in Osijek when world number 223 Franko Skugor stunned 26th-ranked Pablo Carreno Busta 3-6, 6-3, 6-4, 4-6, 7-6 (8/6).
Roberto Bautista Agut steadied the ship for Spain with the world 16 breezing past Ante Pavic - ranked at 486 - 6-4, 6-2, 6-3.
Australia became the first team to reach the quarter-finals when doubles pair John Peers and Sam Groth crushed Czechs Jiri Vesely and Jan Satral 6-3, 6-2, 6-2 in Melbourne for an unassailable 3-0 lead.
A day earlier, controversial world number 15 Nick Kyrgios had powered Australia to a 2-0 lead with a 6-2, 6-3, 6-2 win over the 157th-ranked Jan Satral. Rookie Jordan Thompson upset Jiri Vesely 6-3, 6-3, 6-4.
The Czechs, already missing world number 10 Tomas Berdych, were further disadvantaged when experienced Radek Stepanek was forced to withdraw from the doubles with injury.
The 28-time champions Australia could next face the United States, the 32-time winners who were 2-0 up on Switzerland in Birmingham, Alabama. The US went in as heavy favourites after Australian Open champion Roger Federer and Stan Wawrinka opted not to play.
Jack Sock gave the Americans a flying start with a 6-4, 6-3, 6-1 win over veteran Marco Chiudinelli. John Isner followed with a 4-6, 6-2, 6-2, 7-6 (7/1) victory over Henri Laaksonen.
Argentina endured a traumatic start to their title defence when they slumped 2-0 down to Italy despite the fervent support of Diego Maradona.
Playing without Juan Martin del Potro and Federico Delbonis, the stars of their 2016 final victory over Croatia, the South Americans were outclassed at the Parque Sarmiento in Buenos Aires.
A crowd of 2,000, including football icon Maradona, failed to inspire Guido Pella who lost to veteran Paolo Lorenzi, 6-3, 6-3, 6-3. Andreas Seppi, a late call-up for the ill Fabio Fognini, then made it 2-0 with a 6-1, 6-2, 1-6, 7-6 (8/6) win over Carlos Berlocq who was celebrating his 34th birthday.
The winners of the tie will next face either Germany or Belgium, who are 1-1 in Frankfurt.
World number 22 Alexander Zverev crushed Arthur de Greef, the world 143, to pull Germany level after Steve Darcis downed Philipp Kohlschreiber 6-4, 3-6, 2-6, 7-6 (7/2), 7-5 (7/5).
In Ottawa, Dan Evans downed 17-year-old Denis Shapovalov 6-3, 6-3, 6-4 to give Britain, playing without world number one Andy Murray, a lead over Canada. Vasek Pospisil got the hosts back on even terms with a 6-4, 6-1, 7-6 (7/3) victory over Kyle Edmund.
The winners of the tie are likely to next face nine-time champions France who took a 2-0 stranglehold against Japan, who are without world number five Kei Nishikori.
Richard Gasquet swept past Taro Daniel 6-2, 6-3, 6-2 before Gilles Simon overpowered Yoshihito Nishioka 6-3, 6-3, 6-4.