Yes, a Green Sandpiper. The white crescent at the front of the wings mentioned by Wilson is a very useful feature in identifying Common Sandpiper, and note that Common Sandpiper is also relatively longer-tailed and shorter-billed than this bird. Your photo also shows some spotting on the upperparts, which Common would not show. Also the supercilium does not go beyond the eye.
The other confusion, of course, is Wood Sandpiper, but this differs by being slimmer and more elegant (especially the head and neck), more marked above and with a longer supercilium.
