Hosts Spain made smooth progress into the last eight of the Davis Cup Finals but elsewhere in La Caja Magica on Wednesday it proved a more trying day for players, organizers and fans.

World number one Rafael Nadal sealed top spot in Group B for Spain as he crushed Croatia's Borna Gojo 6-4 6-3 to give his side an unassailable 2-0 lead after Roberto Bautista Agut had beaten Nikola Mektic 6-1 6-3.

It ended a woeful few days for reigning champions Croatia, who were without injured talisman Marin Cilic and sacked captain Zeljko Krajan days before the finals. They left with two losses.

Britain endured a torrid opening day of their campaign though, as they scraped past the Netherlands 2-1 in a Group E tie that spanned nearly nine hours on Court 3.

Australia followed Britain on court — two hours late — to play Belgium in a Group D decider and made up the time.

Nick Kyrgios blasted down 22 aces and won 43 of 43 first serve points in beating Steve Darcis 6-2 7-6(9) before Alex de Minaur beat David Goffin 6-0 7-6 just before midnight.

The Australian pair of John Peers and Jordan Thompson conceded the doubles to Belgium after winning the opening game.

Governing body Tennis Australia tweeted that Peers had "wrist injury concerns" as the Lleyton Hewitt-captained team prepare to face Canada in the quarter-finals.

Britain's three-time Grand Slam champion returned to Davis Cup action for the first time since 2016 but almost 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).

The 32-year-old Murray, who returned from hip surgery in June, looked spent at the end of a brutal match as he took his record in Davis Cup singles rubbers to 31-3.

The Dutch hit back as Robin Haase recovered from a set down to beat Dan Evans but Britain emerged victorious as Jamie Murray and Neal Skupski beat Wesley Koolhof and Jean-Julien Rojer 6-4 7-6(6), saving two set points in the second set.

Britain will face Kazakhstan on Thursday with the winners moving through to the quarter-finals. Captain Leon Smith may rest Murray and might even need a breather himself.

"It's one of the longest days I've had sitting in the chair," Smith, in charge in 2015 when Murray fired Britain to the title, said. "It's been another day of incredible drama."

Novak Djokovic, who Nadal pipped to the year-end top ranking, helped get Serbia up and running with an easy win over Yoshihito Nishioka as they beat Japan 3-0 in Group A.

Tuesday's action had wrapped up at almost 2am with Spain's opening win over Russia and Wednesday was threatening to go just as late with Italy's clash against the U.S. to decide the runners-up in Group F also starting two hours late after Germany's 3-0 Group C defeat of Argentina over-ran.

The U.S. team were at the center of controversy after group winners Canada elected to forfeit the doubles rubber of their clash the previous evening after establishing a 2-0 lead.

Should the U.S. beat Italy later, the 6-0 6-0 doubles win they were "gifted" by Canada could potentially help them as one of the two best runners-up who will join the six group winners in the quarter-finals.

Inevitably after such a radical reform of the 119-year-old team event there have been glitches but the third day of competition produced some electric atmospheres.

None more so than Britain's tie with the Netherlands with Murray cheered on by hundreds of home fans waving Union Jacks.

He needed them too in a nerve-jangling final set, admitting afterwards that he was lucky to beat the 23-year-old Griekspoor.

"I am relieved right now," the former world number one said. "I didn't deserve to win that match."

The Asia/Oceania Group I match between India and Pakistan's Davis Cup tie originally scheduled to take place in Islamabad will now be played in Kazakhstan's capital Nur-Sultan, the International Tennis Federation (ITF) announced on November 20.

"The Davis Cup Committee has voted in favour of the tie being hosted by the ITF on neutral ground at the National Tennis Centre in Nur-Sultan (previously Astana) on 29-30 November," The ITF said in a statement.

(With input from Reuters, AFP)