I have heard that the only posuk in ashrei which requires repetition if one did not have kavanah when saying it is פותח את ידךָ. Where is the source for that?
The source is Rabbeinu Yona Brachos 32a, in the name of the Geoinim.
This is brought in Shulchan Aruch Orach Chaim 51:7
The Mishna Brurah there (:16) says it means to say from that posuk until the end of the chapter. Shulchan Aruch HaRav (51:8) implies that saying the single verse is enough.
Kitzur Shulchan Aruch (14:2) implies that the single verse is all that is required as well.