Scotland rallied well in the clash with the Wallabies at Murrayfield to secure a respectable 31-14 scoreline.
But centre Andy, who made his international comeback after a year out, knows they face another stiff test this weekend.
Andy told today's Evening Times: "Although the boys were disappointed to lose the Australia game, we were delighted with how we played in the second-half.
"We were 28-0 down at half-time and looking at a heavy defeat. So to beat them 14-3 after we came out again was encouraging and restored some pride.
"But it will now be fatal if we start thinking: 'Well, we must be good because we did well against Australia.' We have got a difficult game against Japan coming up.
"They are nobody's fools as we saw in the World Cup last year when they ran us very close indeed. We will come unstuck if we start looking ahead to the games against Australia and South Africa."
The 28-year-old, who came on for club-mate Graeme Morrison, feared he had won his last cap for his country earlier this year when he was in the depths of an injury nightmare.
Andy spent four months out with a knee injury and then another four after he broke down during his rehabilitation. Andy admitted: "There were times during my time out that I thought I had played my last game for Scotland. You are pretty quickly forgotten about.
"There were a lot of good young players, like Tom Phillip and Graeme Morrison, who were getting their chance in my absence. It was good to have quality players like that coming through for Scotland, but demoralising for myself.
"My wife and I made the decision in the summer to move up to Glasgow so I could get back in the picture. That has now been vindicated.
"The English-based players will be involved now, starting with Japan, so I will have to work hard to keep my place. But I'm hoping to get a run."