Cubs 3, Cardinals 0: Junior Lake went 3-for-3 with a two-run homer and Jake Arrieta pitched 5 1/3 scoreless innings in his season debut as host Chicago won its third straight with a milestone victory over St. Louis.Arrieta struck out seven and allowed four hits before Brian Schlitter (1-0) and three other relievers bridged the cap to closer Hector Rondon, who got the final three outs for his third save. Anthony Rizzo homered for the third straight game as six Cubs pitchers combined on a shutout in a nine-inning game for the first time in franchise history.Michael Wacha (2-3) lost for the third time in four starts for the Cardinals, giving up two runs and striking out six in six innings. Matt Adams had three hits for St. Louis, which fell under .500 (15-16) with its ninth loss in 13 games.Chicago snapped the scoreless deadlock against Wacha in the sixth inning when Starlin Castro led off with a single to center and Lake hammered a two-out, two-run shot to left-center to double his RBI output from the previous 13 games.Rizzo, who grounded out with the bases loaded in the fifth, provided an insurance run with a leadoff homer in the eighth off lefty reliever Randy Choate, lining a shot into the seats in right field. The blast capped a three-game binge in which Rizzo slammed three homers to go with six RBIs, six runs scored and six walks.GAME NOTEBOOK: Castro is 12-for-28 since he was moved into the cleanup spot in the batting order. ... Adams registered his 14th multiple-hit game, which leads the National League and tied him for the best in the majors with Mike Trout and Alexei Ramirez, who both play later Saturday. ... The Cubs placed OF Ryan Sweeney (hamstring) on the 15-day disabled list and selected the contract of OF Chris Coghlan from Triple-A Iowa on Saturday. LHP Zac Rosscup was also optioned to Iowa to make room for the activation of Arrieta.