ST. LOUIS — Kolten Wong came through with the bases loaded. When faced with the same predicament, Lance Lynn minimized the damage.
"I told myself, don't get beat by the fastball," Wong said. "It was one of those where you hit it and you know you hit it with everything you've got, so if it doesn't go out it's a tough time."
Wong connected on a 3-2 fastball from rookie Raisel Iglesias (1-3) with two outs in the fourth, putting St. Louis ahead 4-1. Wong's second career grand slam easily cleared the right-field wall, landing in the home bullpen.
Iglesias said through a translator he struck out Wong the prior at-bat on "two bad pitches," but the St. Louis leadoff man didn't bite the next time.
"He made the adjustments really fast," Iglesias said. "So I have to come back with something hard in the middle, and you saw the consequence."
The Cardinals have won six of seven. They are a big league-best 64-35 and lead the NL Central by 6 1/2 games.
Lynn (8-5) allowed one run and five hits in seven innings, improving to 7-3 against the Reds. He has won five of his last six decisions overall.
"My fastball command was terrible tonight, all night really," Lynn said. "But I was able to make pitches when I needed to."
Trevor Rosenthal earned his 31st save in 33 chances after getting two days off.
Jay Bruce hit a bases-loaded sacrifice fly in the third for the Reds, who have lost seven of 10.
"We didn't do our job when we had the chance to, and they did their job," Billy Hamilton said. "When we get those chances, we've got to come through like Wong did."
The starting pitchers combined to hit five batters. The dugouts were warned in the sixth after Iglesias, who hit three batters, plunked Peter Bourjos for the second time. Iglesias hit two in 34 2-3 innings prior to this start. The Reds have had 46 games started by rookies.
The Reds loaded the bases with none out in the third before Bruce's sacrifice fly. The next batter, Brayan Pena, grounded into a double play.
"Bases loaded with a guy that's done damage on me and they only get one, it was a good inning," Lynn said.
Yadier Molina doubled and Stephen Piscotty singled to start the fourth. Bourjos was hit by a pitch, loading the bases with one out ahead of the slam by Wong — also his 100th hit.
"There's just a few people in the league at that position with that skill set that he has," Cardinals manager Mike Matheny said. "He gets in that big spot, he has a lot of faith in himself that he's going to get that done."
Cardinals: Molina felt ill after taking a foul ball in the facemask off the bat of Todd Frazier in the fourth and was replaced by pinch-hitter Tony Cruz in the fifth. Cruz stayed in the game and caught. "After the foul ball my stomach started feeling bad," Molina said. "It was nothing in my head, just the stomach." ... Randal Grichuk was out of the lineup after tweaking his groin Sunday. An MRI showed no serious injury, and Matheny said Grichuk might get another day off, too. Matt Holliday got a regular day off.
Mike Leake (8-5, 3.78 ERA) is 6-9 against the Cardinals but beat them in April, allowing two runs over eight innings. Jaime Garcia (3-3, 1.69) is set to come off the 15-day disabled from a groin injury and make his first start since June 24.