'Worst situation': Rafael Nadal hits out in ugly ATP Cup controversy

A visibly agitated Rafael Nadal has delivered a backhander to organisers of the $21 million ATP Cup, complaining about scheduling after he suffered a rare singles defeat and Spain just scraped through to play Australia in the semi-finals.

The world No.1 was not at his best on Friday - and into the early hours of Saturday, losing in straight sets to Belgium's David Goffin and going down a set in the deciding doubles rubber.

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With partner Pablo Carreno Busta the Spaniards eventually won the match in a super tiebreak, Roberto Bautista Agut's earlier singles victory ensuring the favourites progressed to the last four.

But Nadal was from happy.

Rafael Nadal reacts after losing a point against David Goffin. (Photo by Matt King/Getty Images)

At first he complained about the lack of ventilation in Ken Rosewall Arena but quickly broadened his attack to the tournament scheduling.

"David played a great match. Better than me. I was suffering a lot physically today. Was big humidity," he said.

"But at the same time it is fair to say that we are in the worst position to play the final eight, because we came from Perth.

"That's these three hours' time changing, different weather conditions, playing against a team that have been here for the last ten days, and we are the only team coming from Perth and playing until the last day of Perth and arriving here during the evening with jet lag, with everything.

"And today we had very heavy conditions out there, so probably we had the worst situation possible to play this tie."

Rafael Nadal and Pablo Carreno Busta celebrate their doubles victory. (Photo by WILLIAM WEST/AFP via Getty Images)

Russia's Daniil Medvedev had also complained about his side's move from Perth on Thursday, saying he'd slept only five hours in two days and that the conditions were very different on the eastern seaboard.

He did however win his quarter-final singles match in Sydney, helping his side through to the last four.

Several players have struggled when changing cities, Australian Alex de Minaur notably completely missing a smash against Great Britain's Dan Evans, appearing to lose the ball in the surrounds of the new roof.

Nadal suffers shock loss but Spain advance

The fleet-footed Goffin scored the biggest upset of the ATP Cup with his 6-4 7-6 (7-3) win over the world No.1, but it wasn't quite enough to prevent Spain moving through to a semi-final against Australia on Saturday night.

With Roberto Bautista Agut getting Spain on the board with a 6-1 6-4 opening singles win over Kimmer Coppejans, it then came down to the doubles.

In another gilt-edged rubber, Nadal got back in the winner's circle, combining with Pablo Carreno Busta for a thrilling 6-7 (9-7) 7-5 10-7 win over plucky pair Sander Gille and Joran Vliegen.

Earlier, Novak Djokovic also led Serbia into the semis, eking out a tense 4-6 6-1 7-6 (7-4) comeback win over Denis Shapovalov of Canada.

The world No.2's stirring win followed Dusan Lajovic's 6-4 6-2 rout of Felix Auger-Aliassime and propelled Serbia into a clash on Saturday against Russia.