CHICAGO -- Addison Russell's fly ball in the eighth inning Sunday might be the most important play in baseball so far this year.

St. Louis star catcher Yadier Molina suffered a sprained left thumb on the play as the Cubs ran themselves out of late scoring chances and the Cardinals ended Chicago's five-game winning streak and avoided a sweep with a 4-3 win Sunday.

The Cardinals moved six games ahead of Chicago in the NL Central. The Pirates beat the Dodgers on Sunday to remain four games behind St. Louis.

Molina was injured tagging out Anthony Rizzo on Russell's sacrifice-fly attempt in the eighth. Right fielder Jason Heyward had the assist, throwing out Rizzo on the no-out, bases-loaded fly for a double play.

Molina said he'll have an MRI on the thumb Monday.

"I'm concerned," manager Mike Matheny said. "We're anxious to hear what the doctor is going to report."

Matheny went out to talk to Molina after the play, but Molina remained in the game for the remainder of the half inning before being replaced for pinch-hitter Matt Adams the next inning.

"It hurts (gripping the bat) a little bit," Molina said. "I just couldn't grip it."

The Cubs ran into another out in the ninth. Starlin Castro led off with a single, but pinch-runner Quintin Berry was thrown out trying to steal second by Molina's replacement, Tony Cruz.

Trevor Rosenthal then struck out Jorge Soler and got Kyle Schwarber to ground out for his 46th save in 48 chances.

Despite falling short in this one, the Cubs won four of their final six regular-season games against the Cardinals.

"I could not be more proud of our guys," manager Joe Maddon said. "It's obvious we're playing on the same level as they are right now."

St. Louis became the first team to clinch a postseason berth -- its fifth straight -- on Saturday when San Francisco lost.

The Cubs are comfortably ahead of the Giants for the final wild-card spot. And if they advance in the postseason, there's a good chance they'll face the Cardinals at some point.

"Obviously, the ultimate goal is through them," Cubs starter Jon Lester said.

Carlos Martinez (14-7) pitched four-hit ball into the seventh and allowed two runs. Rookies Tommy Pham and Stephen Piscotty homered.

In the eighth, the Cubs loaded the bases on a single and two walks, then Cardinals reliever Jonathan Broxton walked in a run. Rosenthal entered and struck out Miguel Montero to end the threat.

Martinez retired 11 straight at one point and finished with six strikeouts. His only trouble came in the third, when he walked two then allowed a two-run single to Rizzo.

Lester (10-11) labored despite entering the game with a string of three solid starts in which he allowed four runs in 21 innings. He allowed four runs in six innings while striking out seven.

Lester was 1 for 2 at the plate. He's 3 for 11 against St. Louis and 0 for 82 against all other teams.

Pham, the game's second hitter, launched a drive down the left field line over the bleachers onto the street. It was his fifth homer of the season and fourth in his last six games. One out later, Piscotty lined a two-run shot to left.

TRAINER'S ROOM

Cardinals: 2B Kolten Wong, hit by two pitches Saturday, said he was not injured, but was upset "by the fact that not once, but twice, I got hit."... OF Randal Grichuk, who was on the DL in August with an elbow injury, "is still limited" in the distance he can throw, according to Matheny.

Cubs: Maddon said reliever Pedro Strop was not available after the righty bailed the Cubs out of a ninth-inning jam Saturday and preserved a 5-4 win.

Maddon also delivered on a promised "day at the beach" to Strop for earning his third save. Before the game, a beach chair -- arranged with bottles of beer in an ice bucket, a margarita and other paraphernalia -- was set up in front of Strop's locker.

"I wanted to really make it really emphatic that he was not playing," Maddon said.

UP NEXT

Cardinals: LHP Jaime Garcia (9-5, 2.52) faces Cincinnati LHP John Lamb as St. Louis opens a three-game series and its final homestand against the Reds. Garcia is 6-1 with a 3.02 ERA since Aug. 1.

Cubs: RHP Jason Hammel (8-6, 3.73) takes the mound against Milwaukee RHP Wily Peralta (5-9, 4.41) as the Cubs continue their 10-game homestand. Although Hammel is 2-1 in his last five starts, he's allowed 16 runs in 26 innings for a 5.54 ERA during the span.