ST. LOUIS, OCT. 6 -- Before tonight, it was a lot easier to dismiss Greg Mathews as a left-handed flake in the best Bill Lee tradition.

He's sent dry cleaning out for pickup Monday, when the team left town on Sunday. He's driven his car to the ballpark, forgotten it was there, gotten a ride home then thought his car was stolen the next morning.

But tonight, after learning only upon reaching the clubhouse this afternoon that he would be starting for an injured Danny Cox, Mathews put on the performance of his young career. He struck out seven and gave up four hits in 7 1/3 innings, and the Cardinals defeated the San Francisco Giants, 5-3, for a 1-0 lead in the best-of-seven National League Championship Series.

Mathews even drove in what turned out to be the winning runs, on a two-out, two-run single in the sixth that broke open a close, 3-2 game. Rick Reuschel, 13-9 during the regular season, lost.

Ken Dayley made a save for St. Louis after Cardinals stopper Todd Worrell nearly allowed a game-winning rally in the eighth inning.

But Dayley got Will Clark to fly to right with the bases loaded and two down, then allowed a single in the ninth but made pinch hitter Bob Melvin hit into a game-ending double play.

Cardinals Manager Whitey Herzog said Mathews, 11-11 during the regular season, was told at about 4 o'clock that he would replace Cox in the rotation.

"{Mathews} worked two innings on Sunday and if I would have known Cox would have gotten a stiff neck, I certainly wouldn't have pitched him Sunday," Herzog said. "Under the circumstances, for him to go out there and throw 101 pitches and give us a lead going into the eighth inning is an outstanding effort. I really like his hitting, too."

"He was the difference," Giants Manager Roger Craig said of Mathews, who was making his first appearance in postseason play. "He kept us off balance with his great change-up, and his fastball was just honest enough to be a real effective weapon."

Monday, Mathews prepared for the NLCS by playing golf. He was a bit surprised when he strolled in today.

"I was excited," Mathews said. "This could be the one chance in a lifetime for me. I could get traded. In my second year of pro ball, I'm pitching in the biggest game of my life."

Mathews, who was expected to start Game 4 and see long relief duty in the series, got the start tonight when Cox's stiff neck sidelined him.

Cardinals trainer Gene Gieselmann said Cox woke up Monday with the stiffness and was sent to team physician Stan London for X-rays, which were negative.

"He's been taking treatment in the trainer's room all day," Gieselmann said, "and right now we're shooting for Friday."

Mathews settled down after giving up a first-inning run. First baseman Dan Driessen led off the game with an error that allowed Robby Thompson to reach first. Kevin Mitchell singled to left, moving Thompson to second. Both runners advanced on Jeffrey Leonard's fly to center. Thompson scored on Candy Maldonado's grounder to third baseman Terry Pendleton.

The Cardinals tied the score in the third. Tony Pena singled to left with one down, and Mathews executed his first of two picture-perfect sacrifices, bunting Pena to second.

Vince Coleman grounded a single past Jose Uribe at short to score Pena and make it 1-1.

After Leonard crushed an 0-1 pitch from Mathews in the fourth to the 414 sign in dead center to put the Giants back up, 2-1, Mathews allowed only two singles and a walk until Worrell relieved him with one out in the eighth.

In the interim, the Cardinals retied the game in the fourth. Ozzie Smith tripled to right and scored when switch-hitter Willie McGee, batting left-handed, slapped a single to left with two out.

"You have to be patient to be a good hitter," said Smith, who is now hitting .457 in NLCS play. "You have to guess along with him. I've been guessing right."

McGee, who can barely bat righthanded because of a severely sprained left wrist, said Reuschel's sinker and other junkballs were not as effective as in the past.

"I don't think he was throwing as well as he was capable of pitching, " McGee said. "He threw the ball hard, but I don't think he was keeping it as down as he can."

Meanwhile, Mathews helped himself with the bat in the sixth. Driessen, with a .120 batting average in three championship series, had hit a one-out double to left center.

McGee then hit a ball deep in the hole to short. Uribe had Driessen leaning too far off second, but his throw bounced in front of Thompson and Driessen made third.

Pendleton hit to the opposite field, lifting a high fly down the left field line in front of Leonard. McGee stopped at second and Driessen scored to give St. Louis a 3-2 lead. Curt Ford lined a single to right to load the bases.

One out later, up came Mathews, a .191 hitter (13 hits in 68 at-bats) this season. But after falling behind 1-2, Mathews went after a low offspeed pitch to poke a bloop single into center, scoring McGee and Pendleton to increase the Cardinals' lead to 5-2.

"I'm up there thinking hey, what do I have to lose? I'll take my three cuts. He threw my a slow slider and I just flared at it and it was lucky to hit a hole," Mathews said.

"Greg is a pretty good hitter and he had been pitching well at that point," Herzog said. "If there was one out, I might have taken him out, but don't forget I'm kind of short for pitching with only seven able-bodied pitchers. He didn't mash it but he found an open spot."

Herzog pulled Mathews after he walked Thompson with one down in the eighth. But Worrell could only get one batter before Leonard singled Thompson to third.

Candy Maldonado then just missed a homer to left center off a Worrell fastball. Thompson scored, and the ball bounced into a net in the bleachers just before Leonard rounded third with the run that would have made the score 5-4.

Herzog had seen enough after Worrell walked Chili Davis to load the bases. In came Dayley to face Will Clark, who led the Giants with 35 homers during the regular season. Clark's fly to deep right was caught by Ford just in front of the warning track for the final out.

Uribe singled with one out in the ninth, but Melvin hit a grounder right at Smith. And that made a winner out of Mathews.

"I said, 'Hey, go get 'em, guy,' " Cox said of his pregame advice to Mathews. "He accepted it well. He didn't walk in the clubhouse with his head down or anything."

Herzog's patchwork rotation is now tentatively set with John Tudor going against the Giants' Dave Dravecky in a left-handers' duel this afternoon, followed by Cox Friday in San Francisco, Joe Magrane on Saturday and Mathews again Sunday.

And Mathews, who laughs at his reputation everywhere except on the mound, will try not to order any more $800 suits in Montreal and leave them -- for a year -- to be tailored.