Substitute Beale slipped at the crucial moment when he attempted an 80th-minute penalty from just inside Lions' territory. Had the kick gone over, the Lions would have been left to lament a one-point defeat rather than a gripping 23-21 victory that put them one up in the Test series with two games left.
"In many ways it felt like it was gone when the penalty was given, and obviously we got a bit of luck with Kurtley slipping," Lions fly-half Sexton said.
"If it was the second Test, I am sure there would be massive celebrations, but the way we won it and it is only the first Test, there weren't big celebrations. We know there is one more to go until we do something that will be remembered."
Beale also missed a penalty chance just five minutes earlier, and Sexton added: "In my head, if he had got that I knew we had time at least to go and try to get a drop-goal or a penalty, so that was all I was focusing on then.
"But then with the last kick, the clock was up. Once he had lined that up it was all or nothing. It was win or lose, so it was out of your control then.
"As a kicker, in many ways you don't want to see him slip. If he misses, he misses, but to see him slip is tough on him. It (goalkicking) is a great place when you're going well, and it's a tough place when you miss. He will have a couple of hard days thinking about it, but I feel for him because he slipped."
The Lions prevailed through tries in each half by Wales wings George North - a blistering 60-metre solo effort - and Alex Cuthbert, while full-back Leigh Halfpenny kicked 13 points.
Debutant wing Israel Folau scored both of the Wallabies' tries, but they also accrued a succession of injuries, with centre Christian Leali'ifano, full-back Berrick Barnes and substitute Pat McCabe all carried off.
"It was pretty hectic, pretty crazy out there at times," Sexton said. "It was frantic, tough to control at times, and luckily we have a lot of good leaders in the team that meant we were able to manage the game well at times."
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