You could use Sigil to edit the ePub directly, that, at least, would spare you having to go to Word. Not much of an improvement, I'll admit.
As for your initial problem... you gave the example
Code:
preceding text from Introduction<br/><span class="ts1">ONE<span class="ts2"><br/>Beginning text of chapter 1.
for what you want to match. Generally, it should be possible to match tags in a regexp, though, of course, the regexp won't "understand" those tags other than as a string. In your example, the expression
Code:
<span class="ts1">[A-Z]+<span class="ts2"><br/>
should match the chapter headings.
EDIT: Oh, I'm sorry, I misread your post. I'll have to put the thinking cap back on.