Sainz was stuck in the garage until the final minutes of the session after reporting brake-by-wire problems on his Ferrari.
He came back out in time to attempt one flying lap, which propelled him from last to first.
"It was a very stressful Q1 in these conditions," Sainz smiled. "Obviously, not ideal to be able to do only one lap in Q1 and to put it on P1 was a pretty heroic lap.
"Without knowing how the track was at the time, having no idea how much grip to find, to put it there with only one lap was a pretty good feeling."
Sainz ran out of fresh soft tyres for Q3 and had to settle for fifth on Saturday afternoon's sprint grid.
"I was quite quick in Q2 on the used tyres and also in Q3, but just due to the problem we had yesterday in Q2 we didn't have any softs left, which we know around here is three to four tenths, so that's why we are P5," Sainz added.
After heavy overnight and morning showers, the Red Bull Ring had dried up just in time for the F1's sprint shootout, but reduced grip levels and damp kerbs still made qualifying for the second sprint of the 2023 season hazardous, with teams having headaches on which tyres strategy to use with the sets of news slots they still had available.
While team-mate Leclerc did have a set of softs available for Q3, he said his choice to only have one cool-down lap instead of two between his two flyers cost him as he slotted in behind Sainz in P6.
"I probably didn't do great job managing Q3," Leclerc admitted after qualifying eight tenths behind dominant poleman Max Verstappen, while he was only half a tenth behind in Friday qualifying for the grand prix.
"I asked for push-cool-push, where maybe a push-cool-cool-push would have been better.
"One cool-down wasn't enough, my tyres were extremely hot, so on the second lap I just didn't have enough grip, which is a shame but it's like this.
"Honestly the pace wasn't great this morning in those conditions. The car was much trickier compared to yesterday."
Leclerc is hoping the track conditions will either be full dry or full wet in Spielberg for him to be able to move up the order and challenge the likes of Lando Norris and Nico Hulkenberg ahead.
He will have even more work to do after being handed a three-place grid penalty for impeding Oscar Piastri's McLaren in Q1, dropping him from sixth to ninth on the grid.
Speaking before the penalty was announced, he said: "I hope it's either all dry or all wet, because if it's half and half like this unfortunately there's only one line, from there there's basically nothing we can do.
"Let's see later on if we have good pace and it's all dry we can definitely come back."
