Theriot hit his third homer in four games and 10th of his career, helping the Cubs beat the San Francisco Giants 4-2 on Monday night for their season-best fourth straight win.
Theriot hit a two-run drive in the second inning. He entered the month with just seven career homers, never more than three in a season.
In Friday's 8-6 win over Florida, Theriot ended a streak of 620 at-bats without a homer by hitting his first career grand slam.
"For a guy who is not known for his power it's pretty cool to see," said Ryan Dempster, who pitched seven sharp innings, "and the biggest part of it all is that we've won all those games and he's kind of put a jump-start in a lot of the guys and it's a lot of fun."
"I have been a little inconsistent at times," Dempster said. "Tonight it was good to be a little bit more consistent and throw the ball where I wanted to on a regular basis."
Jonathan Sanchez (1-2) gave up four runs and five hits over four-plus innings for the Giants, but it was Theriot that caught him by surprise.
"I don't go out there thinking I have to get this guy out," Sanchez said. "I didn't know he was that hot. For a small guy, I thought he was going to be a groundball or flyball. You don't give up a lot of home runs like that.
"I was comfortable pitching to him. It was a good pitch but it wasn't in, in. He was cheating on it. He was looking for fastball and he got it."
"Philosophy is still the same," he said. "I'm going to continue to do what got me here and that's to take the ball the other way and get on base and the homers will come."
Sanchez, who hadn't allowed an earned run in his last 12 2/3 innings before Monday's game, gave up a leadoff double to Soriano in the first. With two outs and the bases loaded, Sanchez walked in a run on a 3-2 pitch to Geovany Soto.
With runners on first and second and no outs in the fifth, Sanchez's night ended when right fielder Randy Winn lost Soto's ball in the lights. Soto ended up with a single and Sanchez left with the bases loaded. Reed Johnson followed with a sacrifice fly off Justin Miller.
Giants manager Bruce Bochy is looking for more output from his offense.
"We've got to get runs. The last couple games we've struggled to get runs," he said. "The pitching has been fine. Now it's time to get some runs on the board. That's what has to happen."
Cubs slugger Aramis Ramirez was back after being out of the starting lineup for nine games with a left calf strain. He went 0-for-2 with two walks.
The Cubs placed RHP Carlos Zambrano on the 15-day disabled list with a strained left hamstring and called up utility INF Bobby Scales from Triple-A Iowa. Scales hit .303 in 21 games for Iowa. ... Manager Lou Piniella said the Cubs plan to call up RHP Randy Wells from Triple-A Iowa on Friday to take Zambrano's spot in the rotation at Milwaukee. Wells will be making his first major league start. He made four appearances as a reliever for the Cubs in 2008. ... The Cubs also released reliever Luis Vizcaino.