Andre Schurrle and Mesut Ozil scored in extra-time as Germany claimed a 2-1 win in the round of 16 clash at the Estadio Beira-Rio in Porto Alegre.
The European side perhaps should have sealed the result in regulation time but Low was pleased to see them get the job done regardless.
"In the end it was a victory for willpower," he said after his side reached the quarter-finals .
"In reality, we should have decided the game in normal time. We created a lot of chances.
"In extra-time all the players were at their limit. Sometimes in tournaments you have matches like this where you have to fight until the end."
Schurrle flicked in a Thomas Muller cross in the 92nd minute before Ozil struck just before the end, only for Abdelmoumene Djabou to score a consolation goal for Algeria.
The North Africans looked dangerous on the break and Germany goalkeeper Manuel Neuer came off his line regularly to clear long passes behind his defence.
Low said the Bayern Munich shot-stopper was instructed to come off his line.
"It's good that Neuer comes out and intercepts balls," he said.
Germany face France in the quarter-finals in Rio de Janeiro on Friday.
