The doubles match ended 4:04 a.m.in the Spanish capital (10:04 p.m. ET, 0304 GMT), the latest finish in U.S. Davis Cup history and second in tennis history behind Lleyton Hewitt's victory over Marcos Baghdatis at the 2008 Australian Open, which ended past 4:30 a.m. local time.
"I think in any kind of format that I've ever seen anyone play for their country, they go out there and leave it all out there", he said.
With Russia having beaten defending champions Croatia 3-0 on Monday there was some anxiety on the Spain bench when Rublev surged back to beat Wimbledon semi-finalist Roberto Bautista Agut 3-6 6-3 7-6 (0) and put them ahead.
"I don't even know where we are, what time it is, what day it is", USA team captain Mardy Fish said.
Two separate line calls went against Serbia and left the pair infuriated, while Djokovic also called out the trainer due to issues with his elbow before his team pulled through to take it 6-4 and force a decider.
'I think they should have played the tie'. Where Canada may have felt that that was a dead rubber in theory for them because they were already through, that could have implications to all of the teams potentially that might finish in second place.
A first victory in 10 meetings with Australia means Canada will face either Serbia and Novak Djokovic or Russian Federation in the last four on Saturday, for a place in Sunday's final.
While there have been plenty of teething problems for the inaugural version of the revamped Davis Cup, the knockout phase looks enticing as world number one Rafael Nadal bids to lead Spain to the title on home soil. "It's tough to play Benoit, he is a very talented guy, very unpredictable". France, Belgium, Kazakhstan and the USA were eliminated as the other runners-up.
Serbia, the 2010 Davis Cup champion, was trying to return to the semifinals for the first time since 2017, when the team lost to eventual champion France.
Djokovic added: 'Looking long-term, I personally don't think that the two events can co-exist six weeks apart. I thought we fought hard.
Former world No.1 Andy Murray was given a day off after his near three-hour win against Dutchman Tallon Griekspoor 24 hours earlier but his replacement Kyle Edmund beat Mikhail Kukushkin 6-3 6-3.
Three-time Grand Slam champion Andy Murray returned to Davis Cup action for the first time since 2016 but nearly came unstuck against 179th-ranked Dutchman Tallon Griekspoor, clawing back a 1-4 deficit in the deciding set to win 6-7 (7) 6-4 7-6 (5).
Germany won Group C by defeating Chile 2-1 thanks to a doubles win by Kevin Krawietz and Andreas Mies over Marcelo Tomas Barrios and Alejandro Tabilo.
"Actually, it was pretty special because it was the first time I hear myself singing La Marseillaise", Herbert joked.
The new Davis Cup Finals is being played in World Cup-style with all 18 teams playing in a single venue in the same week. "Winning both ties after singles and not being really pressured by the doubles".