United enjoyed 80% possession, but they could not break down a rigid Albion team that Pulis lined up in a very compact 4-5-1 formation.

Pulis played with four centre-halves at the back and the five-man midfield rarely venture over the half way line to support lone striker Saido Berahino, but crucially they escaped with a 1-0 win.

Chelsea manager Jose Mourinho accused West Ham of playing “19th century football” when they employed similar tactics in January. But the Portuguese’s former mentor at Barcelona refused to go down the same line on Saturday night.

“Every club has the right and also the obligation to beat your opponent in your way and also the best way and the best way to do that is how he did it,” the United manager said.

There were 26 attempts on goal from the hosts, but it was only until the last quarter that Boaz Myhill had much to do in the Albion net.

The 32-year-old saved a penalty from Robin van Persie to keep his team ahead and he denied the Dutchman again – and Angel di Maria – with two stunning saves at the death.

United have failed to score in their last three matches and that is a major concern for Van Gaal.

“We have played 94 minutes only attacking and we have fought until the end, but unfortunately we didn’t scored out of many chances and that is a big disappointment,” he said.

“As a manager I cannot explain that.”

A few weeks ago, United seemed certain to qualify for the Champions League, but they are now just four points above Liverpool with three matches left.

Van Gaal believes it is vital his players keep their spirits up despite going on their worst run of successive league defeats since 2001.

“You need to keep the confidence,” he said.

“That is important when you lose three in the row – then it’s very critical in the heads of my players. I was the only one that said it shall be a rat race until the end.

“I am not happy with that but we are still four ahead so we have everything in our own hands.”

While United sweat about their Champions League place, West Brom are a bit more relaxed knowing that their Premier League status is all but assured.

They are seven points above the drop zone with three matches to go.

“This is a massive, massive result for us,” Albion boss Pulis said. “To come here you have to be resilient. We worked very hard to make sure people were in the right slots, make sure we were in good positions, good areas. But we also needed a bit of luck. And we had that.

“It’s now 10 clean sheets since I arrived. But the key to staying up is to get points.”