"It's one of those things where you play those percentages and hopefully they work out for you," said Weaver, who will start Thursday against the Padres' David Wells.
The 30-year-old Weaver started the year with the Angels and struggled to a 3-10 record and a 6.29 ERA in 16 starts. He was traded to St. Louis on July 5 to make room in the rotation for his younger brother, Jered.
But Jeff continued to struggle as a Cardinal, going 2-3 with an ERA near 6.00 through the end of August. He got hot at the end of the year, winning three of four decisions in September with a 4.15 ERA. The lone loss was a 1-0 heartbreaker to the Pirates in which he surrendered one run in seven innings.
"When he first got with us, he had a couple tough games, but he got better and better and his starts were on the road," said La Russa, who conceded that the home-road splits played into his decision.
"For some reason, I've always kind of started slow and worked into things and then finished strong," Weaver said. "Overall, it was finally not going out there and thinking about everything. [I'm] not thinking about what my mechanics should be, what I should be throwing here, what might be going through my mind at the time. I was able to get into a nice rhythm and not worry too much.
"It's kind of funny. When you don't think about too much out there and you just let things happen, you're a lot better off."
By tabbing him for Game 2, La Russa said he also plans to go with Weaver for a potential Game 5, which would be back in San Diego next Monday.
Weaver, who pitched two full years for the Dodgers before this season, has made nine career starts against the Padres and is 3-4 with a respectable 3.64 ERA in those games. But he is 1-2 in three career starts at PETCO Park, allowing 14 earned runs in 16 innings.
"This is a park that plays deep for the most part and enables you to be aggressive out there, attacking hitters and putting the pressure on them to put the ball in play and make something happen," Weaver said. "I think that they've got a lot of guys who put the ball in play with a lot of consistency, so getting ahead and making quality pitches early in counts is going to be huge. They're a scrappy team. They're going to make it hard on you."
Weaver appeared twice in relief for the Yankees against the eventual world champion Angels in 2002 and was a teammate of left-hander Wells. Four years later, the two will face off.
The end of the regular season and the beginning of the postseason means another fresh start for Weaver, who said the confidence shown by La Russa and Cardinals pitching coach Dave Duncan keyed his late-season turnaround.
"When you start off as rough as I did, you're working your tail off to right the ship and get things going in the right direction," Weaver said. "I think a lot of it had to do with the change itself, getting to St. Louis and being able to start fresh.
"When you come to a new team and you start out a little rough, you can't help but look over your shoulder and wonder what your teammates and coaches are thinking," Weaver said. "It definitely helps to get through those times ... when you have the support of your pitching coach and your manager."