A round-up of results from Davis Cup matches played on Saturday and Sunday
Novak Djokovic suffered his first Davis Cup defeat in five years as Serbia slipped 2-1 down to Kazakhstan while Andy and Jamie Murray gave defending champions Great Britain a 2-1 lead over Japan.
According to AFP, world No 1 Djokovic and 39-year-old Nenad Zimonjic lost their doubles rubber to Kazakhstan's Andrey Golubev and Aleksandr Nedovyesov in Belgrade in the first round tie on Saturday.
The 6-3, 7-6 (7/3), 7-5 scoreline gave Kazakhstan a 2-1 lead ahead of the reverse singles on Sunday where the winner will go on to face either Britain or Japan in July's quarter-finals.
Djokovic will play Mikhail Kukushkin on Sunday when he will try to keep the tie alive for the 2010 champions. The final singles is due to feature Viktor Troicki against Nedovyesov.
In Birmingham, the Murray brothers edged Britain closer to the quarter-finals with a 6-3, 6-2, 6-4 win over Japan's Yoshihito Nishioka and Yakutaka Uchiyama.
It was a fifth win in five Davis Cup outings for the Murrays who didn't face a break point on Saturday.
The win gave the hosts a 2-1 lead and world number two Andy Murray can seal the tie on Sunday when he faces Japan's top player Kei Nishikori, ranked number six, in the first reverse singles.
Dan Evans is scheduled to face Nishioka in what may be the decider.
Nishikori is the highest-ranked player Murray has ever played in Davis Cup, but he has won five of their previous six matches.
"I played well against him last year. I played him a couple of times. He's ranked six in the world, so he's one of the best," said Murray.
"It's obviously going to be extremely tough, but I'm playing well and hopefully I can play a good one tomorrow and try and seal the win."
Elsewhere, John Isner fended off Australia's Bernard Tomic 6-4, 6-4, 5-7, 7-6(4) on Sunday to book the United States a berth in the Davis Cup quarter-finals for the first time in three years.
The world number 11's win on a steamy afternoon at Melbourne's Kooyong Lawn Tennis Club sealed the tie 3-1 with a singles rubber in hand, while silencing a raucous crowd of yellow-clad fans.
"Our team prepared very, very well and I think it showed out here," Isner, who closed out the contest with his 49th ace on match point, said courtside.
The win will take some heat off US captain Jim Courier, who came into the tie on the back of two first-round exits from the team tournament.
The Lleyton Hewitt-captained Australia lost young gun Nick Kyrgios to a virus in a major blow in the lead-up but Isner led off superbly for the Americans with a dominant win over Sam Groth in the opening singles.
He also appeared set to cruise to another emphatic win on Sunday before wobbling when serving late in the fourth set.
Tomic finally broke the towering American on the fifth set point but neither player offered a look at the other's serve in the decider.
Isner's chief weapon would ultimately prevail, as he blasted a string of huge serves to seal the tiebreak and condemn Australia to a first round exit after their run to the semi-finals last year.
The US will next face either 2005 champions Croatia or Belgium in the quarter-finals.
Croatia went ahead 2-1 in Liege when Ivan Dodig and Franko Skugor enjoyed a 7-6 (7/5), 6-3, 6-1 win over Ruben Bemelmans and David Goffin.
Italy became the first team to reach the quarter-finals when Simone Bolelli and Andreas Seppi defeated Marco Chiudinelli and Henri Laaksonen 6-3, 6-1, 6-3 for a 3-0 win over Switzerland.
Italy, whose only Davis Cup title came 40 years ago, will face either Argentina, three-times runners-up since 2006, or Poland.
Switzerland, the champions in 2014, were without Roger Federer, who is injured, and Stan Wawrinka, who opted not to play in the tie in Pesaro.
World Group rookies Poland fought back in Gdansk by winning the doubles against Argentina after dropping both of Friday's singles.
Marcin Matkowski and Lukasz Kubot saw off Carlos Berlocq and Renzo Olivo 6-3, 6-4, 6-4.
In Hanover, Tomas Berdych claimed a 50th Davis Cup win when he and veteran Radek Stepanek claimed a 7-6 (9/7), 7-5, 6-4 win over Germany's Philipp Kohlschreiber and Philipp Petzschner.
The Czech Republic, champions in 2012 and 2013, are 2-1 in front.
If they win through on Sunday they will face France, who beat Canada 3-0 in Guadeloupe, in the quarter-finals.
Jo-Wilfried Tsonga and Richard Gasquet defeated Vasek Pospisil and Philip Bester 7-6 (7/4), 6-1, 7-6 (7/4) for the winning point as France marked captain Yannick Noah's first match of his second spell in charge with victory.