Performance of synchronize section in Java

I had a small dispute over performance of synchronized block in Java. This is a theoretical question, which does not affect real life application.

Consider single-thread application, which uses locks and synchronize sections. Does this code work slower than the same code without synchronize sections? If so, why? We do not discuss concurrency, since it’s only single thread application

Update

Found interesting benchmark testing it. But it's from 2001. Things could have changed dramatically in the latest version of JDK