CHICAGO -- Two of the St. Louis Cardinals' top prospects were on display, and even manager Mike Matheny had to admit he was excited.

And the offense backed up the rookies to beat the best team in baseball.

The Cardinals scored six runs in the eighth inning en route to beating the Chicago Cubs 8-4 and snapping their 11-game winning streak on Saturday.

Starting pitcher Luke Weaver made his major league debut, and Alex Reyes, another top prospect, earned his first big league victory after pitching three scoreless innings.

"Its fun for our organization to see two kids like that just jump in here in this atmosphere at this time of year and be able to do what they did," Matheny said. Randal Grichuk hit his first career grand slam in the eighth on his

25th birthday to cap the Cardinals' rally. St. Louis took a one-run lead on a wild pitch when Yadier Molina struck out with the bases loaded against Carl Edwards Jr. (0-1).

"I'm definitely thankful for being up here right now and getting the opportunities, and I'm definitely trying to take advantage of it," Grichuk said.

Edwards walked the next two batters to bring in another run. Joe Smith replaced Edwards and allowed the grand slam, Grichuk's 14th home run. Edwards walked four in the inning.

"Every one of them is important, but you can't help but get caught up in the atmosphere," Matheny said about the win. "The team is really on a roll, and they've got a lot of things going right for them.”

Ben Zobrist and Addison Russell singled against Seth Maness in the ninth. Maness then committed a throwing error on Jason Heyward's infield single, allowing a run to score.

Zach Duke replaced Maness and got Willson Contreras to fly out. Javier Baez's grounder scored another run before Jorge Soler grounded out to end the game.

Brandon Moss and Jedd Gyorko also homered for the Cardinals, who had have won five of 11. St Louis (61-56) leads the National League with 160 home runs.

The Cubs, who have the best record in the majors at 73-42, saw their longest winning streak since 2001 snapped.

Starter Kyle Hendricks tied a career high with 12 strikeouts but fell short of improving to 9-1 at Wrigley. He allowed two runs and five hits, including two home runs, in seven innings.

Hendricks struck out three in each of the first two innings.

"He was outstanding; he had great stuff again," Cubs manager Joe Maddon said.

Weaver's major league debut was over after 85 pitches. He allowed two runs in four innings after he was promoted from Triple-A Memphis on Saturday morning.

"My first inning was definitely the highlight of my baseball career," Weaver said. "It happened the way I would have liked to write it up. Emotions were just crazy in that moment.

"I just had to take a deep breath and make sure I was in the moment there. But besides that, it was just a lot of fun. I settled in."

Weaver, who replaced injured Michael Wacha in the rotation, was 15-9 with a 1.78 ERA in 197 2/3 minor-league innings.

"Just real impressed with his demeanor, repertoire," Matheny said.

Weaver struck out the first two batters he faced, Dexter Fowler and Kris Bryant, and got Anthony Rizzo to pop out, but ran into trouble in the second inning. Russell homered following Zobrist's double for a 2-0 Cubs lead.

Russell has a career-high 14 home runs this season. The Cubs loaded the bases, but Bryant grounded out to end the inning.

"I was nibbling a little on the strike zone," Weaver said. "Got into deep counts. They did a good job of laying off and having good at-bats."

Reyes, another highly touted prospect, replaced Weaver and struck out three in three scoreless innings in his Wrigley debut and second

major league game. He received a celebratory shower.

"It's intense," Reyes said about the atmosphere. "The fans are great. Just going out there and being able to help the club win a game is awesome.”

Reyes is glad to be reunited with Weaver again after they were teammates in the minors. "Last year, I would start one game, and he would start the next,"

Reyes said. "Being here on the big club and being able to contribute is absolutely fun. There's no other way to put it."

Moss homered off Hendricks in the sixth to cut the lead to 2-1. It was Moss' second home run of the series, and he leads the Cardinals

with 20.

Gyorko's 17th home run tied the game in the seventh.

"Just two bad change-ups, really, two change-ups up (in the strike zone)," Hendricks said. "That was about it. Hopefully, we could keep that winning streak going, but we'll start a new one tomorrow."

NOTES: The Cardinals placed OF Matt Holliday (broken thumb) on the 15-day disabled list and purchased the contract of RHP Luke Weaver from Triple-A Memphis on Saturday. Holliday was injured on Thursday when he was hit by a pitch. ... Cubs RHP Pedro Strop (meniscus tear in left knee) visited the clubhouse on crutches after undergoing surgery Friday. He is expected to be out 4-6 weeks. ... Cubs setup man Hector Rondon (sore right triceps) is doing well and getting closer to pitching, Cubs manager Joe Maddon said. Rondon has not pitched since Aug. 2. ... Maddon said he remains optimistic that INF Tommy La Stella will return to the team. La Stella has refused to report to Triple-A Iowa after he was optioned July 29. He is on the temporary inactive list.