The Rangers held a 2-1 lead heading into the seventh but scored five times to break it open. Jeff Francoeur's solo homer tied it and Julio Borbon drove in a run on a bunt single before Guerrero erased all doubt with a three-run double.
Guerrero was 3-for-5 with four RBI and Francoeur had three hits and drove in a pair for Texas, which collected 18 hits and reduced its magic number to clinch the American League West to two.
Tommy Hunter (13-4) won for first time in four starts, yielding one run on six hits on 5 1/3 innings, walking none and striking out four.
Oakland's Bobby Cramer (2-1) took the loss, allowing four runs on eight hits over six innings.
Jeremy Hermida went 4-for-4 with an RBI for the A's.