ST. LOUIS — Starlin Castro hit one of Chicago's three solo homers and Félix Doubront pitched seven strong innings in his National League debut, sending the Cubs to a 5-1 victory over the slumping St. Louis Cardinals in the opener of a day-night doubleheader Saturday.
Logan Watkins and Chris Valaika also connected for Chicago in the makeup of a May 14 rainout. The last-place Cubs hit four home runs Friday, giving them seven in two games against the Cardinals.
St. Louis has lost four in a row for the second time this season. The Cardinals began the day one game ahead of Atlanta and 1 1/2 up on Pittsburgh for the second NL wild card.
Chris Coghlan had a two-run single for the Cubs, who have won nine of 13.
Doubront (1-0) scattered seven hits in his return from the disabled list. He had been out with a strained right calf since Aug. 1, two days after Chicago acquired him from Boston, where he was 2-4 this season.
The left-hander made his last start for the Red Sox on June 20. He earned the win in relief against St. Louis in Game 4 of last year's World Series.
Justin Masterson (2-3) gave up three homers and five earned runs in 4 1-3 innings for St. Louis. The right-hander was 4-6 when he was obtained from Cleveland on July 30.
Masterson has allowed four or more runs in five of his six starts for the Cardinals and pitched five innings or fewer in four of his starts.
Tyler Lyons struck out eight in 4 2-3 scoreless innings of relief for St. Louis.
The Cubs took a 2-0 lead in the second, when an out at the plate was overturned on replay. Doubront drew a walk to load the bases before Coghlan singled to right. Plate umpire Alan Porter initially called Valaika out at home on a throw from Randal Grichuk.
But a replay showed Valaika had his hand on the plate before he was tagged by catcher A.J. Pierzynski. Chicago challenged and the call was overturned.
St. Louis got a run back in the second when Jhonny Peralta scored on a double play.
Watkins hit the first pitch of the fourth for his first major league home run. Two pitches later, Valaika sent a shot into the left-field bullpen, giving the Cubs a 4-1 lead.
Castro led off the fifth with his 14th homer, matching his career high.
Relief pitcher Jason Motte (lower back strain) threw a bullpen Friday and the Cardinals hope he can return in September. With the minor league season ending this week, there will be no time for Motte to work out the kinks during a rehab assignment. Michael Wacha (right shoulder strain) will pitch Sunday in Tulsa for Double-A Springfield. Wacha went on the disabled list after his June 17 start.
Marco Gonzales (0-2, 7.07) was scheduled to pitch the nightcap. He was called up as the 26th man on the roster to make his fourth major league start and first since July 6. John Lackey gets the ball Sunday. Lackey is 2-1 with a 4.50 ERA in five starts for the Cardinals since being traded by Boston. He is 13-8 with a 3.77 ERA overall.