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SAN DIEGO -- The San Diego Padres are quickly running out of chances to stay in the playoff race.

Alfonso Soriano homered twice, including a two-run shot off struggling San Diego ace Mat Latos, and the Chicago Cubs won 5-2 on Tuesday night to drop the wilting Padres 1 1/2 games behind Atlanta in the NL wild-card race.

The 22-year-old Latos, who fumed after the Cubs scored two unearned runs in the fifth, lost his fourth straight start, his worst stretch this season.

Padres have lost 21 of 32 games since Aug. 25, when they were 76-49 and had a 6 1/2-game lead over the Giants in the NL West. The Padres dropped two games behind the Giants, who beat Arizona 4-2 to reduce their magic number to four for clinching the division. After two more games against the Cubs, the Padres will close the season with three games at San Francisco.

"Here's the deal -- we know where we are. We've got to play good baseball," manager Bud Black said. "We've got to get the bats going. We have to score some runs and hopefully we break out tomorrow and this could get contagious through the lineup. We have to play good defense, we have to do everything to win a game. And that's what we've done the entire year."

The Padres were four-hit for the second straight night, this time by Ryan Dempster and two relievers. Dempster (15-11) struck out nine in seven innings. Carlos Marmol pitched the ninth for his 36th save in 41 chances, and his 20th since the All-Star break.

The Padres lost 1-0 to Carlos Zambrano and the Cubs on Monday night.

"Our season is kind of lost, but opportunities like these are exciting because we're going up against a team fighting for a playoff spot," Dempster said.

Before his skid, Latos (14-9) set a major league record with 15 straight starts of five or more innings with two or fewer runs allowed. In his last four starts, he's allowed 18 earned runs in 16 innings (10.13 ERA), and hasn't made it out of the sixth inning.

"I know I gave up four runs but I felt like the old me," Latos said.

With the score tied at 2 and Xavier Nady aboard on a leadoff single in the sixth, Soriano homered into the Padres' bullpen beyond the fence in left-center. It was his 23rd. Latos got Blake DeWitt to fly out to left, then was hit on the right calf by Koyie Hill's comebacker, which went for an infield single. Latos stayed in the game, allowed Dempster's sacrifice bunt and then was pulled in favor of lefty Joe Thatcher, who got the final out.

"Soriano is a good low-ball hitter and I gave him exactly what he wanted," Latos said.

Soriano homered again on full-count pitch from Mike Adams leading off the eighth.

Latos allowed four runs, two earned, and seven hits in 5 2/3 innings. He struck out six and walked two.

A Padres' defensive meltdown led to the Cubs scoring two unearned runs in the fifth. Latos barehanded Hill's one-out bunt but dropped it for an error. Dempster sacrificed over Hill, who scored on Kosuke Fukudome's double to left-center. Starlin Castro beat out an infield single deep in the hole at shortstop as Miguel Tejada tried to make a twisting, off-balance throw. The ball skipped past sprawling first baseman Adrian Gonzalez and into the Padres' dugout, allowing Fukudome to score.

"I should have fielded it with my glove and not my bare hand," Latos said. "I didn't rush it but I felt like I could have taken my time. It hit my palm and took off."

Black agreed, saying Latos should have gloved the ball.

As for Tejada, "Miggy was trying to make a play," Black said. "When you spin and throw, it's a do-or-die play. I'm all right with that because he was trying to make a play."

An upset Latos was yelling at someone in the dugout after the inning.

San Diego's Nick Hundley tied it at 2 with a 398-foot home run on a full-count pitch from Dempster into the second deck in left field, his eighth. Chase Headley was aboard on a one-out walk.

Moments after homering, Hundley tried to calm down Latos in the dugout.

At nearly the exact moment Hundley connected, Juan Uribe hit a trying solo home run leading off the fourth to pull the Giants into a 2-2 tie.

Dempster allowed four hits and walked two. The Padres had two runners on and no outs in the seventh before Dempster struck out the side.

"They have plenty of life left," Cubs interim manager Mike Quade said. "They have two more games at home against us and then they get to settle things in San Francisco."

Game notes

Padres OF Will Venable missed his second straight start with a sore lower back, similar to the injury that landed him on the DL earlier this season. ... Dempster struck out nine for the fifth time this season. He became the third Canadian-born pitcher with at least three 15-win seasons. The others are Fergie Jenkins (10) and Russ Ford (3). ... The Cubs, fifth in the NL Central, improved to 16-8 in September.