Wales led 23-22 before replacement playmaker Harries struck the vital penalty with the very last play of the game.
Deans knows losing the series will hurt the Grand Slam champions, especially given the nature of the 25-23 defeat that left them just seconds away from a first victory on Australian soil in more than 40 years.
"I am expecting a response from Wales - they came here with high expectations and with good reason," said Deans, who believes the second-Test heartbreak will make Wales an even tougher proposition when they face off in three days time.
"They'll obviously be devastated that the series is over. As a player you want to be winning it or in it right to the end.
"So they will be devastated that it's over and that will make them dangerous, just as it will make us dangerous, because both sides will be unshackled.
"There's no doubt that defeat in Melbourne will make them stronger. There's two options. You curl up and walk away or you come back better for it. They will come back. You could see that in their faces."
Deans also feels there is plenty more to come from the Wallabies, though, after they scraped to victory at the Etihad Stadium.
Australia have since been boosted by the return of star full-back Kurtley Beale as they look to secure a series whitewash and a fifth successive win over Wales in the past eight months.
And with the key goal of three-match rubber now already in the bag for the reigning Tri Nations Champions, Deans is hoping to add some style to substance on Saturday.
"It's great to have taken the series out now with the two wins but it's a great opportunity to play some better rugby," added Deans.
"We've really got to push on and show some more attacking rugby and actually use the ball a lot more.
"We haven't played the best in the last two games and we know that. So we were pretty lucky to come up with the win after coughing up so much ball and giving them that one pretty easy try."