Russia down Djokovic and Serbia in thriller to book Davis Cup semifinal spot
With the their quarterfinal tie level at 1-1, Rublev and Khachanov edged out the Serbian pairing 6-4, 4-6, 7-6 (8) after an a epic third-set tiebreak in which the Russians had been forced to save three match points.
It had been a tempestuous match after Djokovic at one stage fired a ball into the stands in anger at calls which went against him.
Earlier in the day, Russian youngster Andrey Rublev got his country off to the perfect start when he swept Filip Krajinovic aside in straight sets, 6-1 6-2, in their singles match.
But 16-time Grand Slam champion Djokovic pulled his team level when he defeated Karen Khachanov 6-3 6-3 in their match, meaning it was all set up for decisive doubles rubber.
Ominously for Russian pairing Rublev and Khachanov, Djokovic appeared for Serbia alongside Viktor Troicki.
But it was the Russians who took the first set 6-4, before Serbia fought back to claim the second by the same scoreline.
The match saw tempers flare however as Djokovic and Troicki erupted at two line-calls which went against them, with Djokovic launching a tennis ball into the stands and getting a warning for his troubles.
Djokovic was forced to save break points on his serve in a tense third set which went to a tiebreak.
It was the Russian pair who held their nerve, winning the breaker 10-8 and taking the match and the tie with it.
It is the first year of the $3 billion revamp to the Davis Cup, labelled 'The World Cup of Tennis' and spearheaded by Barcelona and Spain football star Gerard Pique.
Eighteen countries started out in Madrid, divided into six groups from which the top teams and best second-placed finishers progressed.
Serbia had won two from two in their group round robin, while Russia had beaten reigning champions Croatia and lost to a Spain team led by world number one Rafael Nadal.
However, it was the Russians who secured their spot in the semifinals where they will face Canada, who beat Australia 2-1 in their quarterfinal tie.
Later on Friday Argentina will play Spain and Great Britain will meet Germany as they bid to reach the last four.