Why doesn't my TL071CP op amp act as a voltage follower?
To expand on the comments a little: A TL071 is the wrong opamp for the configuration you're using, because you've exceeded the "Common-Mode Input Voltage Range" spec.  

If you go to Table 6.3 on page 6 of the datasheet and look for the Vicr (Common-mode input voltage range) line you'll see that with a +15V/-15V supply (that's 30v from + to -), the minimum guaranteed input voltage range is +-11V. That's 4V away from each supply.  

So, with your single 9V supply and the same rule applying, your input voltage must lie in the range of 4 to 5V in order for the opamp to behave properly. The 2.5V from your voltage divider is clearly out of range.

Even if you look at the more lenient data from the 'Typical' column, the range is -12 to +15 with +15/-15V supplies and this would lead to an input range of 3V to 9V with your single 9V supply. So your 2.5V input is still out of range.

Try to find an opamp which is intended to run from a single-supply (like an LM358) and you should see much better results.