CHICAGO -- The St. Louis Cardinals are in such a hitting funk these days, one big swing against Michael Wacha was enough to beat him.
The defending NL champions lost for the fourth time in five games and slipped below .500 this season, falling to the Chicago Cubs 3-0 Saturday.
"You got to grind. You got to push through this," Cardinals manager Mike Matheny said. "That's the philosophy of our offense when we're going right, and we'll have to fight our way through."
Junior Lake and Anthony Rizzo homered, leading Jake Arrieta and the Cubs to their season-best third win in a row.
A day after the Cubs tagged St. Louis ace Adam Wainwright, they came back to beat Wacha (2-3). Wacha allowed two runs on five hits in six innings, with both runs scoring on Lake's two-run shot in the sixth.
"Just the one homer there put a couple of runs up," Matheny said. "But that's still a great day for him. We just have to do what we keep talking about and try and get some offense. It's just not coming."
St. Louis, which stranded eight runners, has scored two runs or fewer in seven of its last 13 games. The Cardinals got seven hits, and were shut out for the fourth time this year.
"Right now, it's not looking like what we want it to look like," Matheny said. "Whatever we're doing is not working, so we have to figure it out and figure it out fast."
Along with his third homer, Lake also doubled in going 3 for 3.
"It's just frustrating, really," Wacha said. "I was pitching well and if I was able to get out of a jam there ... But I served one up there and they go up two runs. You just can't afford that in that situation."
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The Cubs have their longest winning streak since a three-game sweep of San Francisco in late July.
Arrieta struck out seven over 5 1/3 innings in his season debut, giving up four hits. The right-hander was activated from the disabled list before the game, having been out because of shoulder stiffness.
Chicago's bullpen combined to pitch 3 2/3 scoreless innings. Brian Schlitter (1-0) got two outs for the win.
Yadier Molina and Jhonny Peralta opened the St. Louis ninth with singles off Hector Rondon. But he got Jon Jay to hit into a double play and struck out Mark Ellis for his third save.
"Getting the first two guys on against the closer is a good opportunity, but double plays definitely hurt," Matheny said. "Our guys are going up there with an aggressive approach looking for one in their zone, but on one pitch definitely took a little wind out."
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Rizzo led off the eighth with sixth home run, and third in three games. He connected on the first pitch he saw from Randy Choate.
Arrieta walked two and threw 82 pitches. The Cardinals put five runners on base through the first three innings, but escaped.
Arrieta struck out Molina to strand runners on the corners in first. The Cardinals put two on with no outs in the second before Greg Garcia struck out, Wacha grounded out and shortstop Starlin Castro made an over-the-shoulder catch on Matt Carpenter's popup.
The Cubs loaded the bases in the fifth, and Wacha fell behind in the count 2-0 against Rizzo before getting him on an inning-ending grounder.
NOTES: Cardinals LHP Jaime Garcia (shoulder) is scheduled to make a rehab start Saturday at Double A-Springfield.
