Cahill volleyed in the opener for Holger Osieck's side just before halftime and substitute Robbie Kruse tapped in the second on the hour.
''I was happy that it was a preparation for our upcoming (World Cup) qualifiers,'' Osieck said. ''I tried a couple of things with guys in different positions and I got some good impressions from that.
''We moved the ball pretty well and played some decent football. We had a good structure defensively when Wales tried to build up, but they did not have the means to break through despite their individual class.''
Darcy Blake pulled a goal back in the 82nd minute for Wales, which was at near full strength as Tottenham winger Gareth Bale made his first international start since last October.
''When we were in possession we always had support for the man with the ball and it looked pretty decent considering we are at an early stage of the season,'' Osieck said. ''The win is a bonus as it is always important to win as you gain a lot of confidence from that.''