Mauricio Pochettino branded the Video Assistant Referee system a “nightmare” after Tottenham cruised into the FA Cup semi-finals with a 3-0 win at Swansea.

A double from the outstanding Christian Eriksen and an Erik Lamela strike secured Spurs a last-four tie at their temporary Wembley home next month.

But the victory was not without controversy as, with Spurs 1-0 ahead, Son Heung-min’s 23rd-minute goal was ruled out for offside.

The incident was reviewed at length by VAR and, with the lines on the television proving inconclusive as to whether Son was offside or not, the original decision stood.

“It’s a nightmare. I feel so sorry for the people trying to use that system,” said Pochettino, who had also seen VAR dominate proceedings in the fifth-round replay against Rochdale.

“I think I prefer it when the ref and assistant make mistakes than to wait three or four minutes for things.

“But we now need to see the reality of how it is going to affect the staff on the touchline and the officials.

“It is so complex, but the worst thing for me is the effect for the fan.

“It is going to be a massive problem for the future. We will see what happens at the World Cup.”

Spurs were without the injured Harry Kane as Pochettino made seven changes from the side which had won at Bournemouth the previous weekend.

Dele Alli, Mousa Dembele and Hugo Lloris were all left on the bench but there was no way back for Swansea in their first FA Cup quarter-final for 54 years after Eriksen’s superb 11th-minute opener.

Lamela added a second in injury time at the end of the first half before Eriksen scored again just after the hour mark to raise hopes of a first Tottenham trophy since 2008.

“He is fantastic, so important for us,” Pochettino said of Eriksen.

“Every season he takes one step up, he is so consistent.

“(A trophy) is an option now.

“At the same time, just when you feel close to winning something, then you can be far away.

“We are going to try to win the semi-final and get to the final. Of course, it would be fantastic for the club to win a trophy.”

Swansea had won seven straight games at the Liberty Stadium since losing to Tottenham in the league at the start of January.

But the absence of the Ayew brothers – Jordan was suspended and Andre cup-tied – blunted their attack, while their midfield and defence could not cope with Tottenham’s subtle movement.

“I am not disappointed,” said manager Carlos Carvalhal, who had always insisted Swansea’s battle to stay in the Premier League was their priority.

“The FA Cup has been a fantastic run for us – our best since 1964 – and this has not created any harm or damage for the future.

“We lost to a quality team who played well and scored fantastic goals.

“I said before to achieve something we must be at our best and they must be not so good.

“We know there is a gap and that they are better.”