CHICAGO -- During the offseason, Rockies catcher Chris Iannetta rebuilt his throwing from the basics. From maintaining his balance, to taking the proper steps, to having solid arm action, nothing escaped his attention in trying to build the perfect throw.

The fundamentals paid off for Iannetta twice during the team's split with the Cubs, when he caught Alfonso Soriano trying to steal second in Monday's 4-0 loss, and Kosuke Fukudome at second in Wednesday's 5-2 victory.

But the true test of a player's fundamentals comes when conditions aren't perfect. Iannetta passed that one at a key time Wednesday.

With no outs and runners at first and second in the ninth in Wednesday's game, pitcher Jason Grilli bounced a pitch that Iannetta blocked, but the ball squirted several feet to his right. Iannetta pounced on it, then threw a strike to third to beat Mike Fontenot, who was trying to run. Despite the extraordinary circumstances, Iannetta wound up with his normal three-quarter arm delivery and his weight properly shifted toward the target.

Grilli forced the next hitter, Geovany Soto, into a game-ending double play.

What was best about it was that Iannetta didn't think about it. Asked the hows and whys of his body positioning, the catcher said that they never crossed his mind in the moment.

"I just threw it," Iannetta said. "I really don't know what happened. ... That's not really what I worked on this offseason. I just tried to make a good throw."

Iannetta and the Rockies hope success becomes second nature as well.

Last season, Iannetta threw out 16.3 percent of baserunners on stolen-base attempts. His career percentage is 17.1. As a comparison, the Brewers' Jason Kendall led the Majors at 42.7 percent.

This year, according to STATS Inc., Iannetta has thrown out three of four baserunners, with all the action coming in the last three games. That's not counting the play against Fontenot, who wasn't considered trying to steal, because he didn't take off until the ball was in the dirt.

The Phillies' Chase Utley was successful, but Iannetta caught Jayson Werth on Sunday, and he caught Soriano on Monday and Fukudome on Tuesday. Iannetta also had success this spring. The offseason work seems justified.

"It's helped, so far," Iannetta said. "We'll see where it goes the rest of the year. That's going to be the big test, how it holds up over 162 games. We'll see."

It would be the next step in Iannetta's development.

With little experience, Iannetta had the job at the start of 2007, but lost it to Yorvit Torrealba. He then spent some time at Triple-A Colorado Springs and finished with a .218 batting average. Last year, Iannetta took over the job from Torrealba in May and finished with a solid offensive season -- a .264 average, 18 home runs, 65 RBIs and a .390 on-base percentage.

Although Iannetta hasn't shown much early-season offense in 2009 -- he is 1-for-17, the hit being a home run, with five walks and seven strikeouts, and he has to work on not hitting under balls -- the Rockies have confidence he will improve based on last year's results.

But the confidence in Iannetta's defense is growing.

"I've known that about Chris," Grilli said. "I have every bit of confidence in him and Torrealba. You want to try to bury a pitch with guys on base, you know that Chris is going to keep the ball in front of him. He did a great job of that, and recovering."

Manager Clint Hurdle said, "To go 10 feet and get a ball, throw it 115 feet and get an out at third base, that's a big play. Chris is doing a fine job behind the plate and throwing the ball as well as he ever has."