Shawn Camp relieved, and his first pitch to Chris Denorfia was inside and bounced off the glove of Welington Castillo, who failed to hustle after it as the ball rebounded off the brick wall. Blanks at first hesitated, then ran home with the tying run.
"I want to apologize to my teammates for doing that, that's not going to happen anymore," Castillo said. "I feel like I lose the game. I'm the one that has to keep everyone in the game and I just got out of the game."
Denorfia walked, James Russell relieved and Everth Cabrera grounded a single to center for a 3-2 lead, San Diego's first lead since Tuesday. It was the Padres' only hard-hit ball of the inning.
Chase Headley followed with a slow roller past the mound toward second and reached on a run-scoring infield hit.
"It's one of those things where, regardless of what the situation is with the outs or what the score is, you can always take advantage of the mental lapses that go on on the field," Blanks said. "That's just a testament to nobody here giving up."
Thatcher (2-0) pitched one-third of an inning for the win. Huston Street allowed a two-out double to Nate Schierholtz in the ninth, then struck out pinch-hitter Luis Valbuena for his sixth save in six chances.
Wood (2-2) gave up three runs and four hits in 7 2-3 innings. He has won two of six starts despite a 2.50 ERA.
Stults allowed two runs and seven hits in 6 2-3 innings. He had been 0-3 with a 7.24 ERA at Wrigley Field.
On a raw afternoon, the gametime temperature was 45 — about 25 less than Wednesday — and the wind was blowing in from the north at 19 mph.
Chicago failed to take advantage of its early chances and went 0 for 7 with runners in scoring position.