ST. LOUIS (Ticker) -- Mark Prior has bad news for the National League - he can get better.

The budding superstar won his fifth straight start by firing eight scoreless innings as the Chicago Cubs opened a key three-game series with a 7-4 victory over the St. Louis Cardinals.

Prior remained perfect since returning from the disabled list, allowing one run - a solo homer to Albert Pujols - and three hits with a walk and six strikeouts. He threw 116 pitches, 76 for strikes.

A darkhorse in the Cy Young Award race, Prior (13-5) is 5-0 with a 0.69 ERA in his last five starts, allowing only 21 hits and four walks while striking out 35 in 39 innings.

"I'm just trying to pitch," the soft-spoken Southern Californian said. "Things aren't as sharp as I'd like them, but I'm still making pitches and that's the important thing. I'm not blowing guys away, but my pitch count is down."

Prior, the second overall pick in the 2001 draft, lost his only appearance against the Cardinals last year. But in three meetings this season, he is 1-1 with a 2.42 ERA.

"He's throwing 94 miles per hour, that ball's moving all over the place and he has a good curveball," said Jim Edmonds , who went 1-for-3 against Prior. "What can you say? He's one of the best young pitchers in the game."

Prior's teammates staked him to a huge early lead, scoring six runs in the third inning, as the Cubs remained within one-half game of Houston for first place in the National League Central Division. St. Louis fell a game off the pace.

"It's a big win when you can have a big inning here and start the series off," Cubs manager Dusty Baker said.

The Cubs managed five hits and a walk in the sixth. Kenny Lofton doubled in the first run and Ramon Martinez singled him home. After a walk to Sammy Sosa and flyout, Simon swatted a high-and-away fastball to the opposite field in left for a three-run homer.

"I didn't know the pitch was high, I just tried to hit the ball hard," Simon said. "Everytime I go out there, I try to hit the ball hard someplace. That's the way I approach myself, that's my plan."

"You make a pitch to Simon, the way he hit it, I thought it was a foul, a double or is caught," Cardinals starter Garrett Stephenson said. "Once that happens, with Prior pitching, the game is pretty much over."

Aramis Ramirez followed Simon by hitting the next pitch over the center field wall for his 20th homer.

Since being acquired from Pittsburgh, Simon is 10-for-27 with two homers and nine RBI. He had been best known for hitting a fan in an Italian hot dog outfit with a bat during a sausage race at Milwaukee's Miller Park.

"You watch this guy take batting practice and he has a powerful, electric bat," Baker said. "However, I'm going to play whoever I think is best that day. That's a sign of a good team."

Stephenson (7-13) allowed six runs and five hits with a walk and a strikeout in three innings. In 27 starts this season, he has surrendered 30 homers, one behind teammate Brett Tomko and two others for the major league lead.

"It's been my downfall pretty much most of this year," he said. "I'm giving up the long ball. Four out of the six runs were on home runs. You're not going to win a game when you're facing Prior and give up six runs."

One run is a lot against Prior, who retired 10 of the first 11 batters he faced and set down the side in order on 12 pitches after his team gave him six runs. He got six straight outs until Pujols' two-out homer in the sixth.

"It makes my job easy," Prior said of the big inning. "I just need to go out and make pitches. It makes it a lot of fun when they go out and put up a big inning."

Pujols hit a first-pitch fastball over the wall in straightaway center field for his 35th homer and first hit in 14 at-bats since he returned from the flu.

"He looked good in practice," Cards manager Tony La Russa said of his star left fielder. "He had real good at-bats. That was the Albert we're used to."

Prior wasn't as impressed.

"(At) 7-0, I'm not going to mess around," he said. "Obviously, I wasn't trying to throw it waist high down the middle. I didn't want to walk him. He's a great hitter, a strong hitter. It's down the middle. He should hit it out."