Tries from Owen Williams and Ashley Beck and seven points from the ever-accurate boot of British & Irish Lion Leigh Halfpenny saw Gatland's side record their second win of the autumn.
But Gatland, who led the Lions to a 2-1 series victory over the Qantas Wallabies in the summer, wants his Welsh contingent to record a win of their own next Saturday.
"We're very confident about the Australia game. We were disappointed with the first game of the autumn against South Africa when we went behind but got back into it," Gatland told Wales Online.
"We showed character in dealing with injuries which in the past we wouldn't have been able to do.
"We built on the positives for Argentina and if we can win next week then three out of four will be a reasonably good return from the campaign.
"It's a nice achievement [100th Test as a coach] but I'll forget the game pretty quickly and it's not a performance I will reflect on.
"The team is the end product and the most important thing as coaches is to try and get the best out of them and hopefully improve.
"It's a milestone but it's not something I am motivated by or think too much about."