The attacker came off the bench to score in extra-time to fire Germany into the last eight but admits that his strike, which went in off his heel, was fortunate
Joachim Low's men were held to a goalless stalemate after 90 minutes by the spirited African side, who went close to scoring on a number of occasions only to be denied by an effective performance from Manuel Neuer.
However, substitute Schurrle struck early in extra-time to give the Germans the lead before Mesut Ozil added a second, meaning that Abdelmoumene Djabou's late goal for the Algerians was a mere consolation.
The Chelsea man believes that his team-mates' profligacy nearly cost them and, though he insists his backwards flick goal was no fluke, accepts that he had a large slice of fortune.
"Obviously we wanted to win the match earlier," he told ZDF. "But Algeria did well, they pressured us from the beginning. I scored almost the exact same goal in Mainz three weeks ago. So I am capable of it, but of course I had a little luck.
"We had many chances in the last 10 minutes of the 90, but we missed them. Now we are at the quarter-finals. We need to relax, and then play France."
Germany will face France in the quarter-final on Friday, with the winner facing either Brazil or Colombia in the lst four.