Just two starts into his major league career, Astros rookie Henry Sosa is still learning how to pitch in crucial situations.

Sosa's mistake to Geovany Soto in the sixth inning cost the 25-year old right-hander a chance to earn victory No. 1.

Soto had three hits and two RBIs and Kerry Wood earned his first save in over a year as the Chicago Cubs won for the 12th time in 15 games with a 4-3 win over the Houston Astros Monday night.

With two on, two out and a 3-1 count to Soto in the sixth, Sosa (0-2) meant to throw a slider off the plate and inside. With the pitcher's spot due up next, Sosa didn't want to give Soto anything good to hit.

"I wanted to throw the slider in," Sosa, who made his first-ever start at home, said. "It was in, but he hit it good enough."

In the sixth, Soto extended the Cubs' lead to 4-1 with a two-out two-run double that scored Marlon Byrd and Reed Johnson, who reached on back-to-back singles.

Astros manager Brad Mills said that was clearly not a situation where Sosa would be going after the hitter with the pitcher's spot due next.

"That is not what we were doing there," Mills said. "It was a pitch that came back. It backed over for him and became hittable. ... That just turned out to be a really big hit."

Sosa allowed four runs on seven hits with six strikeouts in six innings for Houston, which has dropped seven in a row and 10 of their last 11. He set down nine in a row at one point before Marlon Byrd walked with one out in the fourth.

Rodrigo Lopez (4-3) pitched an effective 5 1-3 innings, allowing two earned runs and the bullpen held on for Chicago.

Wood's last save came on June 29, 2010 against Toronto while he was with Cleveland, but he had his club record tying streak of eight straight strikeouts dating back to Aug. 5 broken by Jason Michaels, who flew out to begin the ninth. Wood struck out the last two batters.

Carlos Pena had two hits and two RBIs, and Aramis Ramirez had three hits for the Cubs, while J.D. Martinez was 2 for 3 with two runs scored and Matt Downs had two doubles and two RBIs for Houston.

Pena gave the Cubs a 2-0 lead in the first with a two-run double off the hill in deep center.

Martinez scored in the fourth to cut the lead to 2-1. After Martinez singled to start the inning, Downs hit a one-out double to right. Tyler Colvin's throw to second to try to get Downs bounced off the base far enough for Martinez to score from third.

The Cubs got out of the inning as Brian Bogusevic flied out to Byrd, who fired an on-target throw to third to get Downs trying to advance.

"That was a dumb mistake on my part," Downs said. "I know better than to go on a ball like that."

Downs closed the gap to 4-3 with a two-run double in the sixth that scored Jose Altuve and Martinez and chased Lopez. Downs is 6-for-14 in the Astros' last eight games.

"I guess I was in a pretty bad slump up until about two weeks ago, but I came out of it four or five days ago, and I have felt pretty good ever since," Downs said. "I just feel more comfortable now, and I am getting some pitches to hit."

NOTES: Houston acquired 19-year-old OF Domingo Santana from Philadelphia as the player to be named in the July 30th trade that sent OF Hunter Pence to the Phillies. Santana, who was ranked by Baseball America as the No. 9 prospect in the Phillies' organization, had been playing at Class A Lakewood for the Phillies, and has been assigned to the Astros' Class A Lexington team. ... Cubs recalled LHP Scott Maine from Triple-A Iowa Monday to fill the empty roster left after RHP Carlos Zambrano was placed on the disqualified list Saturday. ... RHP Ryan Dempster (10-8) takes on RHP Brett Myers (3-12) Tuesday in the second game of the three-game series. Dempster is 6-3 with a 3.07 ERA in 12 starts since June 8, while Myers is looking to snap a career-long six game losing streak.