How do you get SED to replace only the first set of characters in a search expression

How do you get SED to replace only the first set of characters in a search
expression

Basically I think this question is more one of regex than SED directly,
but it's SED I'm using, so that's where I'm starting from.
I've got a web.config configuration file for an ASP.NET 2.0 website that
I'm automating the build process for. I'm using UNIXUtils to give me some
extra power over and above that provided by Windows. Using SED can someone
enlighten me as to how I'd accomplish the following;
Change
Data Source=RANDOM-SERVER;Initial Catalog=SomeDatabase;Persist Security
Info=True;User ID=MyUser;Password=*************;
To
Data Source=PRODUCTION-SERVER;Initial Catalog=SomeDatabase;Persist
Security Info=True;User ID=MyUser;Password=*************;
I've tried the following
sed s"|Data Source=.*;|Data Source=PRODUCTION-SERVER;|g"
but what I receive is
Data Source=PRODUCTION-SERVER;
i.e. sed is helpfully being ultra greedy and eating all the characters up
until the last semicolon, at least that's what it seems to be doing.
BTW: Yes I would like to retain the |g greedy operator on the end to
ensure that the alteration is applied to all occurrences in the original
file, though, in theory there shouldn't be.
If someone can show me how to accomplish this I'd be grateful, though I
suspect there isn't an easy way to do it, as I've not been able to find
anything on the net that matches my requirements. Annoyingly everybody's
focused on paths of one form or another.
If it can't be done in SED but can be done using something else in the
standard UNIXUtils suite, then that's an acceptable answer, I'm open to
suggestions.