CINCINNATI — Skip Schumaker watched the ball fly as he headed for first base, unsure whether it had enough to create a little personal history.

Just enough.

Schumaker hit his first career grand slam during the St. Louis Cardinals’ biggest inning of the season Monday night, providing Chris Carpenter with more than enough runs on that one swing to beat the Cincinnati Reds for the ninth time in a row.

The 7-3 win got the Cardinals off to an impressive start in their showdown for first place. St. Louis moved within one game of the Reds, who have been atop the division for the past week.

“It’s a good start,” Schumaker said.

St. Louis sent 12 batters to the plate for seven runs in the fourth, giving rookie Mike Leake (7-4) one of his worst moments in the majors. Schumaker’s grand slam — only his 19th career homer — made it 6-0. The ball cleared the wall in center and landed next to the Reds’ bullpen.

“That’s the first time it’s happened in my career,” Schumaker said. “Everyone gets lucky once in a while. I probably hit it in the right park.”

Balls tend to fly out of Great American Ball Park — though not when Carpenter is on the mound, of course. Carpenter (13-3) has won his last nine starts against the Reds, a streak that started in 2006. He gave up five hits and a pair of runs in seven innings.

“I do the same things I do against anybody else,” Carpenter said, trying to explain the streak.

“I watch video every single time and see what has changed and what hasn’t changed and put something together.”

Ramon Hernandez had three of Cincinnati’s seven hits, including an RBI double off Carpenter and a solo homer off Kyle McClellan.

The crowd of 36,353 was revved for one of the most meaningful series in Great American Ball Park’s eight-year history. The Reds haven’t been in first place so late in a season since 1999, when they were playing at Cinergy Field.

The Cardinals left the fans silently sweating in their seats.

The teams have been locked in a back-and-forth race since mid-May, never separated by more than three games since then. St. Louis leads the season series 8-5. They meet only one more time, for a three-game series in St. Louis from Sept. 3-5.

St. Louis has its top three pitchers set to start against the Reds during their showdown series — Carpenter, Jaime Garcia and Adam Wainwright. The Reds opened with a rookie.

For one of the few times, Leake looked like one.

St. Louis started the fourth with six consecutive hits. The clincher came from Schumaker, who hadn’t played since Wednesday because of a sore left wrist. His fourth homer of the season got Leake uncharacteristically flummoxed.

Leake lost track of outs. He fanned Brendan Ryan for the second out in the fourth, then started jogging off the field. He realized his mistake just before reaching the foul line, turned around and gave up a single by Felipe Lopez. Manager Dusty Baker decided that was enough.

“That was a quick six,” Baker said. “They got six in a span of 12 pitches. It happened so quickly that I didn’t have time to get anybody warmed up.”

In his last two starts, Leake has given up 14 runs (six earned) and 15 hits in 8 2-3 innings. He sat in the dugout with sweaty hair stuck to the side of his forehand and a faraway expression in his eyes.

“The big inning has been that way for the last few outings,” Leake said. “I have to find a way to not do that. When the same thing keeps happening, it’s not fun. I just have to stay focused. I feel great. I’m not tired at all. I’m just hitting a rough patch.”

Carpenter had his way with the big lead, extending his streak of dominating an offense that leads the NL in batting, runs and hits. The right-hander beat the Reds four times last season, and now has beaten them four times already this season.

The Reds brought in another ex-Cardinal before the game, adding outfielder Jim Edmonds through a trade with Milwaukee. Edmonds played for Reds general manager Walt Jocketty in St. Louis. Edmonds started in center and went 0 for 4 with a strikeout.

NOTES: Carpenter is 4-0 in six starts since the All-Star break with a 1.79 ERA. … Albert Pujols extended his hitting streak to nine games. He also walked for the first time in 12 games. … Reds RHP Aaron Harang plans to throw a simulated game on Tuesday, then start a rehab assignment in the minors. Harang has been in the disabled list since July 6 with lower back spasms. … The Reds optioned LHP Travis Wood to Triple-A to create a spot for Edmonds. Wood was going to miss his turn in the rotation because of two days off in the next week.