Can I use 10-speed Shimano STI shifters with a 9-speed drivetrain? I need to replace Shimano 105 STI shifters on a 9-speed road bike which was damaged in an accident, however there are few places that still stock 9-speed Shimano 105 STI shifters.  

Can I use the 10-speed Shimano 105 STI shifters with my 9 speed cassette and derailleur? How well would this work?
I have 10 speed Ultegra shifters working 9-speed Ultegra everything else.

I've not had any problems.

Even the 10-speed cassette went on the wheel with no adjustments needed, nor any adjustments to the derailleur. Surprised me, but it worked.