Novak Djokovic and Andy Murray sprinted through their Davis Cup openers to edge Serbia and defending champions Great Britain closer to a dream quarter-final showdown.
But their teams are still facing a weekend long battle to set-up that July duel after Kazakhstan and Japan fought back to level their respective ties on Friday.
World number one Djokovic showed no signs of the eye infection which brought his run of 17 successive finals to an end in Dubai last week as he brushed past Kazakhstan's Aleksandr Nedovyesov 6-1 6-2 6-3 in Belgrade.
Djokovic, who led Serbia to the 2010 title, required treatment on a left shoulder problem although it did not prevent him from securing an easy win over his 200th-ranked opponent.
"The shoulder is nothing and the eye infection is behind me so I am looking forward to playing the doubles on Saturday," said Djokovic.
Mikhail Kukushkin, the world 79, stunned 23rd-ranked Viktor Troicki 7-5 6-2 6-4 to level the tie at 1-1 as Kazakhstan kept alive their hopes of a fourth successive quarter-final appearance.
Serbia could face Great Britain in the quarter-finals and Murray did his best to keep that clash on track when he saw off Japan's world number 87 Taro Daniel 6-1 6-3 6-1 in just 90 minutes in Birmingham.
But world number six Kei Nishikori then avenged one of the worst defeats of his career as he defeated Dan Evans 6-3 7-5 7-6 (7/3) to bring his country level at 1-1. Nishikori suffered a miserable straight sets loss to Evans in the pair's only previous meeting in the US Open first round in 2013.
Murray was playing for the first time since losing to Djokovic in last month's Australian Open final, opting instead to spend time with new daughter Sophia, born on February 7, and wife Kim Sears.
"The last few weeks have been the best of my life, it's been really, really special," he told the BBC.
Murray and captain Leon Smith must now decide whether he plays Saturday's doubles alongside his brother Jamie, which proved a winning combination three times last year, or whether Jamie partners Dom Inglot.
Australia's Bernard Tomic fought off a challenge from American Jack Sock to level their tie 1-1 in Melbourne.
Tomic looked to be heading for a comfortable victory, rolling through the opening two sets, before being forced to battle hard to win 7-6 (7/2) 6-3 3-6 6-4 on the grass surface of Kooyong.
The victory, in sweltering temperatures, was crucial for Lleyton Hewitt's Australians, who lost the opening singles rubber when Sam Groth went down to world number 11 John Isner 7-6 (7/2) 6-2 6-2.
The winner of that tie will face either last year's runners-up Belgium or 2005 champions Croatia.
Former US Open champion Marin Cilic gave Croatia a winning start in Liege, seeing off Kimmer Coppejans 7-5 6-3 7-5 before David Goffin levelled by seeing off teenager Borna Coric 6-3 6-2 2-6 3-6 6-3.
In Pesaro, Paolo Lorenzi won the longest tiebreak in Davis Cup World Group history to give Italy a 1-0 lead over 2014 champions Switzerland, who are without Roger Federer and Stan Wawrinka.
Lorenzo defeated 34-year-old Marco Chiudinelli, ranked at a lowly 146, in five sets, 7-6 (16/14) 6-3 4-6 5-7 7-5 in a rubber that last 15 minutes short of five hours. The winner will face either Poland or Argentina, who are playing in Gdansk.
Guido Pella defeated Michal Przysiezny 6-1 6-4 7-6 (7/5) to give Argentina, runners-up three times since 2006, an early lead. That became 2-0 when Leonardo Mayer beat world number 602 Hubert Hurkacz 6-2 7-6 (7/3) 6-2.
In Guadeloupe, Yannick Noah's first match in his second spell as France captain got off to a winning start when Gael Monfils eased past Frank Dancevic 6-3 6-1 6-3 in the tie against Canada.
The winners face either Germany or the Czech Republic, champions in 2012 and 2013, in the next round.
World number 30 Philipp Kohlschreiber gave Germany the lead in Hanover with a 3-6 6-3 6-4 2-6 6-3 victory over Lukas Rosol.
Czech number one Tomas Berdych will face 18-year-old debutant Alexander Zverev in the second singles rubber.