The Taegeuk Warriors required two extra-time goals to defeat Uzbekistan in the quarter-finals of the Asian Cup on Thursday, maintaining their 100 percent record in the competition as they head into the final four.
It was forward Son who grabbed a brace to send his side through, and while pleased with the result, Stielike believes his side struggled mentally in the first half.
“We saw a lot of different phases of play in the 120 minutes," he explained.
"Our main objective was to bring the mentality and concentration like we played against Australia to this game, but in the first half we saw mental problems when we played with a lot of pressure.
"We knew whichever team lost would be on the plane home to their country and I think this pressure was our main problem in the first half.
“After half-time we played much calmer with less unforced errors, as in the first half we couldn't play five passes. After 91 minutes there was only one team on the pitch, and with this strong 30 minutes at the end of the game, the victory went to the right side."
Korea Republic have been forced to do without star players Lee Chung-yong and Koo Ja-cheol due to injury, and Stielike believes that they have done exceptionally well to fight on despite the pair's absence.
“I think we can discuss a lot about our technical quality… What we cannot enter into discussion about is the mentality, the sacrifice of our boys," he asserted.
"I am not sure that a lot of teams after three games and with two of their best players out of the competition like us (could compete). A lot of teams would lose their mentality if you take two leaders out of their group."