MADRID -- After having to play in an empty arena in the group stage, Novak Djokovic relished being in front of Davis Cup fans again.
Djokovic fed off the energetic crowd from the start on Wednesday, leading Serbia into the semifinals with a 2-1 come-from-behind win over Kazakhstan at the Madrid Arena.
The top-ranked Djokovic kept Serbia alive in the quarterfinal by defeating Alexander Bublik in straight sets in his singles match, then teamed up with Nikola Cacic in the deciding doubles for a 6-2, 2-6, 6-3 win over Andrey Golubev and Aleksandr Nedovyesov.
Serbia had played its group-stage matches without fans in Austria, because of the coronavirus pandemic.
"It makes a huge difference,'' said Djokovic, who was constantly turning to the crowd to celebrate during his matches. "Fans are one of the reasons why professional tennis exists. Playing in front of the fans is very important. They give us great energy, they give us a lot of motivation to try to play our best on the court. In Innsbruck we didn't have fans so it was a completely different atmosphere.''
Serbia reached the last four for the first time since 2017 and will face Croatia, which got past Italy on Monday.
Serbia broke serve at 2-2 and 5-3 in the third set of the doubles to seal its fifth semifinal appearance in the team event.
Serbia made it to the last eight as one of the top two second-place finishers from the six groups. It was second to Germany in a group that also included Austria.
Serbia lost to Russia in the quarterfinals of the first edition of the Davis Cup Finals in 2019. Its only title came in 2010 in a final against France, and it was runner-up to the Czech Republic in 2013.
Djokovic broke serve once in each set against the 36th-ranked Bublik to win 6-3, 6-4 and extend his singles winning streak in the Davis Cup to 17 matches. He comfortably won his first two matches in this year's edition of the revamped team competition.
Djokovic had 11 break points in total in the match that lasted 1 hour, 18 minutes at the Madrid Arena.
The 182nd-ranked Kukushkin needed more than three hours in his 7-6 (5), 4-6, 7-6 (11) win over No. 69 Kecmanovic. He saved four match points, including two in the decisive tiebreaker.
Kukushkin was a break up in the second set but Kecmanovic came back by winning four straight games to even the match after converting his fifth set point.
Kecmanovic got off to a fast start in the decisive set but couldn't capitalize on his five break opportunities to take a 4-0 lead. He then squandered two match points at 5-3 before being pushed into the tiebreaker. The Serbian needed medical attention at 5-4 but was able to continue.
Kukushkin saved another pair of match points in the tiebreaker before converting his fifth opportunity to clinch the win.
"This is why we love the Davis Cup,'' Kukushkin said. "I'm just honored to play for my country and get the with for Kazakhstan. It was important for us. I'm super excited.''
Kazakhstan was trying to make its first semifinal appearance after reaching the last eight six times -- most recently in 2018 when it lost to Croatia. It won its group this year against Sweden and Canada, the runner-up in 2019.
Viktor Troicki is making his debut as Serbia's captain two years after his last appearance as a player.
It was a mostly packed Madrid Arena for the quarterfinal even though host Spain didn't make it past the group stage. The Spanish capital was the sole host of the team event in 2019, but this time Innsbruck in Austria and Turin in Italy also held matches. Madrid will host both semifinals and the final.
A new venue for next year will be unveiled on Sunday.