The balloons were reminiscent of a favorite spectacle employed by the Flaming Lips, the local heroes who once took Coldplay on as an opening act. During a stripped-down set played at the edge of the stage, Martin thanked Lips leader Wayne Coyne for taking them on a tour of Oklahoma City that day and told the audience there were four great American voices: "Elvis, Dylan, Wayne Coyne and Johnny Cash." Coldplay then launched into "Til' Kingdom Come" and segued into a spirited, rough hewn version of Cash's "Ring of Fire."
Here's a link to reviews of the concert:
http://newsok.com/article/related/2933511/
http://newsok.com/article/keyword/1827973/