How could fire both TextChanged event and button click if button is clicked

[dyw55a]

I am using ASP.NET. I have 3 web server controls on my page. One is
textbox1 with AUTOPOSTBACK = true. The other one is another textbox2
with AUTOPOSTBACK = false. The third item is a save button.

Now, I want whenever textbox1 changes, system automatically fills in
value in textbox2. If user click on button, then system SAVE
information into database.

Now my problem is if when user change text in textbox1, instead of move
cursor ro anywhere else, he click on SAVE button. So the system will
fire page autopostback and fill in value in textbox2 but will not SAVE
this information. I do want to save the information when user click on
SAVE.

I understand that there is one one action server could response to
this. Is there anyway I could detect that user click on button instead
of moving cursor out of textbox1 area?

Thanks in advanced,
Dean