Jake Westbrook has developed a troubling trend that could prove detrimental to the St. Louis Cardinals' playoff hopes.

For the third time in four starts the right-hander allowed runs in the first inning.

Westbrook walked the first three batters of the game and they all scored. The Cardinals couldn't recover, losing 7-0 the Chicago Cubs on Friday.

"I was pretty much all over the place and the walks hurt you, especially when they're in a row with no outs," Westbrook said. "It wasn't very good. . It's always frustrating when you don't give your team a chance to win and do your job which I haven't been able to do the last couple outings."

The Cardinals have lost six of nine and are tied with the Reds, 2 1/2 games back of the first-place Pittsburgh Pirates.

Asked if Westbrook is a certainty to make his next start, Cardinals manager Mike Matheny was non-committal.

"We'll see how he feels tomorrow," Matheny said

"That's not what any of us were looking for," Matheny said. "Talked about it before, sometimes he just has trouble finding the release point for his sinker and he couldn't find it today until it was too late."

The Cardinals couldn't manufacture anything against Jake Arrieta, who threw seven innings of two-hit ball. Arrieta (1-0) struck out seven for his first win with the Cubs.

The hard-throwing right-hander was acquired from the Baltimore Orioles in a July 2 trade. Before Friday, Arrieta's only other day on the Cubs' roster was as the 26th man for a doubleheader against Milwaukee on July 30.

The Cubs snapped a four-game losing streak with the win and are 7-7 this season against the Cardinals.

"I've commanded the ball well, I've mixed my pitches well," Arrieta said. "I kept them off balance, off the heater enough, to get some weak contact. That's the goal."

The Cubs had been shut out in four of their past five home games - a streak dating back to Aug. 3.

Westbrook (7-8) finished with five walks but managed to grind through 6 2-3 innings to save the Cardinals' bullpen. Ultimately Westbrook allowed seven runs - six earned - on eight hits with only two strikeouts.

Since coming off the disabled list June 14, Westbrook is 5-7 with a 5.86 ERA. After the loss, Westbrook said his arm feels fine.

Nate Schierholtz, the Cubs' cleanup hitter, hit a two-run single to center to put the Cubs ahead in the first and after Welington Castillo grounded into a double play, Donnie Murphy followed with a run-scoring single to give the Cubs a 3-0 lead.

Arrieta sailed through the Cardinals lineup. After allowing a single to Carlos Beltran in the second, he got Kolten Wong to ground into a double play in his major league debut. Those two outs started a streak of 13 straight outs (including five strikeouts) until he walked Westbrook with one in the sixth.

The next batter, Matt Carpenter, also walked to give the Cardinals their first threat of the game, but Jon Jay grounded into a fielder's choice and Matt Holiday struck out looking to end the inning.

The Cubs added a run in the fifth on Schierholtz's sacrifice fly and then scored two more in the sixth on a run-scoring double by Darwin Barney and a safety squeeze by Arrieta. They tacked on one more run in the seventh which scored on a wild pitch.

NOTES: Cardinals first baseman Allen Craig said he has a sore left elbow after he was hit by a pitch from Arrieta in the second inning on a 94 mph sinker. Craig stayed in the game and finished 0 for 2 with two strikeouts and a walk. . With the addition of prospect Kolten Wong (who went 0 for 3 in his debut) to the Cardinals' roster and lineup on Friday, former World Series MVP David Freese was relegated to the bench with leadoff hitter Matt Carpenter (who had been playing second) moving to third base. "I would say it's a day-by-day situation," general manager John Mozeliak said. "I'm not saying (Wong) has to play every day - there are gonna be times when we want to get David back in the lineup - so I imagine there's gonna be some split playing opportunities." ... Cubs RHP Matt Guerrier was scheduled to have surgery on his throwing arm on Friday. The surgery, performed by Dr. Timothy Kremchek, is expected to sideline Guerrier six to eight months. ... The Cards' Joe Kelly (3-3) faces Travis Wood (7-9) in the second game of the series on Saturday.