Netherlands coach Louis van Gaal stunned onlookers at Salvador's Fonte Nova Arena by bringing on Krul to replace Jasper Cillessen in the final seconds of extra-time after 120 minutes had finished deadlocked at 0-0.
But van Gaal's audacious move paid dividends as Newcastle keeper Krul saved Costa Rican penalties from Bryan Ruiz and Michael Umana to send the Dutch through the last four.
The Netherlands will now play Argentina on Wednesday for a place in the July 13 final after hosts Brazil face Germany in Belo Horizonte on Tuesday.
The team had won only one penalty shootout in five previous attempts at major championships.
But penalty takers Robin van Persie, Arjen Robben, Wesley Sneijder and Dirk Kuyt all made no mistake from the spot to beat Costa Rica goalkeeper Keylor Navas.
"It's a dream come true for me," said Krul.
"I watched the penalties. We've been preparing with all the goalkeepers and the goalkeeper coach.
Van Gaal later said Krul was introduced because he could