Johan Santana is marching toward an Opening Day assignment April 5 at Citi Field against the Atlanta Braves.

Santana retired the first seven St. Louis Cardinals he faced and took a scoreless effort into the sixth inning in his fourth Grapefruit League start.

Santana, sitting at 88 mph with his fastball, proved that was more than enough velocity to make his changeup effective.

He limited the Cards to six hits -- all singles -- while striking out six and walking none in a 69-pitch effort that included 48 strikes and spanned six innings Wednesday afternoon at Roger Dean Stadium. The southpaw surrendered one run, on an RBI single by Lance Berkman in the sixth, when St. Louis produced three of its hits against him. Berkman's single came on one of Santana's few changeups up in the zone.

"I had a good day," said Santana, who expects to return to Jupiter in five days to again face the Cardinals, in his second-to-last tuneup.

Said Terry Collins: "We talk about the process involved in getting him ready for the season. There are some minor steps. There are some baby steps. And there's some giant steps. And today was a giant step forward. To pitch to that lineup the way he pitched and then to get up and down and recuperate -- outstanding."

Santana -- who also incorporated a solid slider -- had logged no more than 2 2/3 innings in any of his previous starts, although he had tossed 65 pitches in the most-recent outing, when he was charged with five runs (four earned) against the Detroit Tigers.

St. Louis started the eight position players who should be in the lineup Opening Day, albeit in a slightly different order, since the Cards will be facing Miami Marlins right-hander Josh Johnson and not a southpaw. (St. Louis’ projected lineup for the opener is: Rafael Furcal, Carlos Beltran, Matt Holliday, Berkman, David Freese, Yadier Molina, Jon Jay and Tyler Greene.)

"I knew that was going to be a challenge," Santana said. "They're the world champions."

Santana’s changeup appeared in prime form all afternoon. He twice struck out Freese on pitches that caused the Cardinal's bat to go flying into foul territory down the third-base line -- once on a slider, once on a changeup.

"I threw some good ones out there. When I'm able to set everything up, and throw my fastballs and mix my changeups, sometimes that happens," Santana said about the bat-flying episodes. "I'm pretty sure he was trying to hit a ball and I threw the right pitch and he swung and missed. It's good to see those swings sometimes."

In addition to the actual success, Santana achieved a milestone in being able to get up and down for six innings. The last time Santana had pitched that length in any setting was Aug. 28, 2010 against the Houston Astros -- two and a half weeks before undergoing surgery to repair a torn anterior capsule in his left shoulder.

"That was the key," Santana said. "It's not about one inning or that pitch or what they're doing. It's about going deeper in the game and warming up between innings and to come back again and compete and throw your pitches again with the same consistency from the first one all the way to the last one."

All signs point to Santana being able to take the ball on Opening Day in 15 days against the Braves.

"We're going to see the next couple of days how it feels," Santana said. "I've got to throw my bullpen and we'll go from there, but so far it's been good. The way I feel, the way that we have worked from the beginning, everything has been positive. ... Definitely I feel really good mentally and physically that I'll be there. ... We're getting closer. Like I've always said, every time that I go through one day I'm closer to coming back. I'm definitely working my way to be ready for Opening Day. We'll see how everything goes."

Said Collins: "That's the most he's worked in a long time. We'll see in a couple of days how he feels when he does his bullpen and go from there. Obviously we're very optimistic about the way he's worked so hard. ... To be honest, I thought there might be a day where he would say, 'Hey, I want an extra day. I'd like an extra day because I want to get a long-toss program in.' Right from the start -- starting in January, when I came down here in January -- he's never missed a beat. He's done exactly what he's been asked to do, with his own input. But he's never said, 'Hey, look, I want to push this back a day.'

"He's said, 'I feel good and I'm ready to do the next step.'"