Well, wpr is one, I think -- I assume expats count. (-: I'm only an amateur, but I don't disagree with anything he said.
To me 'sightread' (I prefer it without the hyphen) is a lot more common, but 'play/sing sth.
at sight' is also possible. It may help to put an asterisk in the Google search:http://www.google.com/search?hl=en&q=
It's definitely not wrong, but I'm trying to put my finger on how it differs from just sightreading, if at all.
To me it's more like a gradual spectrum. If you can read music, you can decipher the marks on the page. If you can sightread, you can read those marks fast enough to sing or play at the same time you're reading; you not only understand the notes on the page, but can reproduce them yourself. And if you can play a whole piece at sight, you can sightread in public without stops or noticeable mistakes, enough to consider it a genuine performance, if not a perfect one.
Here's a thought: Could you possibly say something like 'vom Blatt durch
spielen/-singen,' to distinguish it from just sightreading?
In English there are actually two different senses depending on the location of 'through':
play/sing sth. (all the way) through = completely, from start to finish, as a whole
play/sing through sth. = give it a casual run-through, a once-over, a practice go
The 'completely' sense is the one I'm thinking of. Is that what was meant by 'abspielen,' to play a whole piece right off, in a sense, at one go? (I don't think 'play at sight' can possibly refer to a card game, BTW.)
I would be interested to hear if other German speakers find 'abspielen' unfamiliar in this context/collocation, as Mattes apparently did.
I don't think 'to read at sight' is right; that would just be 'sightread.'
In fact, you can also say 'sightsing (also: sight-sing),' which might also be worth adding.
But there's no such word as *'sightplay' -- which is perhaps why the alternative version 'play sth. at sight' exists.
In any case, I do agree that 'at sight' is the basic expression and that it doesn't necessarily have to refer to music at all. For example, would you use 'vom Blatt' for 'translate at sight'? LEO already has 'bei Sicht' and 'bei Vorlage,' for comparison.