Guerrero was 0 for 5 before lining a shot deep into the left-center gap off Oakland closer Andrew Bailey (0-1) to drive home Michael Young. Texas (20-15) took two of the three in the series matching the AL West's top teams to build a two-game division lead.
Elvis Andrus led off the 12th with his fourth hit, but was then caught stealing. Young drew a walk and Josh Hamilton had a single before Guerrero's winning hit.
Dustin Nippert (2-3), the loser in the 13-inning series opener Tuesday, worked around a leadoff single in the 12th.
Jake Fox had three hits for Oakland, including a single in the fourth on a pitch from C.J. Wilson that umpires had signaled was a balk. Because Fox hit the ball, the A's by rule got to choose which to take -- so Fox wound up with a base hit and Wilson wasn't charged with a balk.
Wilson got called for another balk in the seventh, when he flinched his body while still on the rubber without delivering a pitch. Home plate umpire Bob Davidson immediately sent runner Josh Donaldson from second to third base. Catcher Matt Treanor kept his mask over his head and was still facing the mound when he obviously said something the umpire didn't like and was ejected.
Rangers manager Ron Washington then had a lengthy discussion with Davidson, but wasn't thrown out of the game. Max Ramirez replaced Treanor behind the plate.
On the pitch before that, Cliff Pennington hit a fly down the right-field line that he and manager Bob Geren both thought was fair and would have gotten Donaldson home. Geren came out to question first base umpire Alfonso Marquez. Pennington eventually grounded out to end the inning.
A balk was being discussed even before the game, when Geren questioned the umpires' postgame decision the previous night that resulted in a balk on Athletics pitcher Gio Gonzalez.
In Oakland's 10-1 loss Wednesday night, Gonzalez was initially charged with a throwing error after he awkwardly stepped off the rubber and threw wildly to the plate when Ian Kinsler suddenly broke from third base. About a half-hour after the game, the umpires called the pressbox and said it was actually a balk.
Geren said Thursday that he thought Gonzalez stepped off correctly before making a wild throw. But the manager added it didn't matter since the run scores either way.
After Fox's balky single in the fourth, Landon Powell walked to load the bases before Donaldson blooped a single to left for a 1-1 tie.
Julio Borbon drew a two-out walk and stole a base in the third before scoring on a single by Andrus, who extended his hitting streak to 13 games, the longest active in the majors.
Wilson struck out five while allowing a run and four hits in seven innings. The left-hander's ERA dipped slightly from 1.51 to 1.48, though he lost the AL lead Wednesday night when New York Yankees right-hander Phil Hughes dropped to 1.38 after throwing seven scoreless innings.
Oakland starter Ben Sheets pitched into the seventh, allowing a run and three singles with eight strikeouts and three walks. Sheets had allowed 17 runs over 7 1-3 innings his previous two starts on the road, when he became the first A's pitcher to give up at least eight earned runs in consecutive starts.
Texas was working on a two-year deal for Sheets before the 2009 season when negotations fell through because of his elbow problems that led to surgery and him missing all last season. The right-hander, the NL starter in the 2008 All-Star game, signed a $10 million, one-year deal with Oakland in January.
NOTES: Texas had two runners thrown out trying to score on infield grounders. Ian Kinsler was cut down in the seventh and David Murphy in the ninth. ... Rangers reliever Frank Francisco struck out all four batters he faced, throwing 17 of his 20 pitches for strikes in the 10th and 11th innings. ... Craig Breslow worked two scoreless innings for Oakland, taking over after the Rangers opened the opened with consecutive singles.