The Galaxy beat the Sounders 3-0 at The Home Depot Center on Sunday thanks to a double from Robbie Keane and go into the return bout at the CenturyLink Field this weekend with plenty of confidence.
Donovan says it is important for the team to maintain the attacking game style which allowed them to produce the victory but suggests that the Seattle side are capable of coming up with a winning score as well.
"We have to stay aggressive," Donovan said.
"I think defensively we were very good, our shape was very good and we really limited their chances.
"But next week they'll have Eddie [Johnson] from the start, my guess is they'll have [injured midfielder Mauro] Rosales from the start, and they're a much different team at home than they are on the road.
"They beat us, 4-0, earlier in the year, and there's no reason why they can't do that again. So we've got to be prepared."