He used the second-half break for water - introduced because of the sweltering temperature estimated at around 35 degrees on the field - to change his formation and the Dutch came from a goal down to win 2-1 with two late goals in the last-16 match. "I first changed to a 4-3-3 and then we created a lot of opportunities with a shot on the post and a fantastic save from(Mexico goalkeeper Guillermo Ochoa).
"Then I moved to plan B and yes, I did that in the cooling break that is a clever way of benefiting from these breaks," he told reporters. A water break in each half is only allowed when the temperature in the stadium is above 30 degrees and is decided on by FIFA doctors. It is pre-arranged with the teams and referees. Van Gaal admitted it was a lucky escape for his side as they edged past Mexico but gave himself and his players a pat on the back for preparation and tactical switches.
"They had faith and believed till the very end," he said. "The humidity was not in our favour. We were fresher and fitter than the Mexicans. "Not only did my players have belief that they could perform today, they also were fit for this match. "Yes, it was an escape but in the second half we showed that we could create more opportunities and we played three different systems."
The Dutch started with their much-debated 3-5-2 formation but after going a goal down early in the second half switched to 4-3-3 with Arjen Robben out wide on the right, substitute Memphis Depay on the left and Robin van Persie in the middle of the attack. "But that wasn't working out either and I could see I need to change again, so I waited for the cooling break," Van Gaal said.
"Did you see what I did?" he asked reporters in the manner of a school master enquiring of his pupils. "Van Gaal brought on target man Klaas-Jan Huntelaar, took Dirk Kuyt out of defence to partner him in attack and had his team pump long balls into the Mexico penalty area.
"It's a big compliment that my players picked up on it immediately. We have a modest group of players but they have outstanding team spirit and this is ultimately what led to the victory." Van Gaal said he was unsure whether key midfielder Nigel de Jong, who went off injured in the opening 10 minutes, would be available for the quarter-final against Costa Rica or Greece in Salvador on Saturday.
"It's a groin injury. He is one of the most important elements in the team, so that was a big drawback, a big setback for us." But captain Van Persie does not have any injury concerns.
"I took him off for tactical reasons," Van Gaal added.
(Writing by Mark Gleeson; Editing by Ed Osmond)