He rebounded in that Sept. 18, 2002, outing by tossing a scoreless inning and eventually earning a spot on the Angels postseason roster.
The rest is October lore, as "K-Rod" was a dominant late-inning presence for the Angels en route to their 2002 World Series championship.
"We've been hearing he had good stuff, but that was the first time we really saw him in person," then-Giants manager Dusty Baker said during the World Series. "For a young pitcher, he throws a lot of strikes, quality strikes."
Rodriguez is the pinnacle of September callup success stories because not only was he a late addition, he also was an oddity -- only eligible for the postseason roster because Steve Green's injury earlier in the year opened a loophole the Angels used to add Rodriguez to the 40-man roster.
Rodriguez isn't the only late-season callup to leave a mark.
Do you remember "Fernandomania," in 1981? Well, Dodgers lefty Fernando Valenzuela showed sign of things to come in 10 relief outings in September 1980, allowing zero earned runs and striking out 16 in 17 2/3 innings.
But September hasn't only belonged to those who take the nation by storm. In fact, the past two World Series champions received Rodriguez-like help in the season's final month as they made their way to the postseason.
St. Louis' Adron Chambers delivered in a big spot last Sept. 16 after entering as a pinch-runner for Lance Berkman. Chambers knocked a single in the top of the 11th for the go-ahead run in the Cardinals' eventual 4-2 win over the Phillies.
"That's a great example of our club," then-manager Tony La Russa said after the game. "If you follow us all year long, you know. Sometimes we're not good enough, but the effort is always outstanding.
"There were a lot of guys shaking hands tonight. They all had a part of it."
A team effort also was what led the Giants to the 2010 World Series title.
Darren Ford is a mere footnote among the "castoffs and misfits" in San Francisco's story that season. But the speedy outfielder gave the Giants a big win the first time he stepped foot into a Major League park.
In his Major League debut on Sept. 1, 2010, Ford stood at second base as a pinch-runner in the bottom of the eighth with the game tied at 1. As the pitch from Colorado's Ubaldo Jimenez hit the dirt, Ford took off for third and a wild throw from the catcher brought him home for the winning run.
True, Chambers and Ford's contributions were small. But it's important to remember how important each game was to the Cardinals' epic comeback, and that the Giants won the National League West on the regular season's final day. As proven the past two years, every play and game is highlighted a bit more in September.
It's not just championship winners that get boosts in September. Future stars also can show potential in summer's final month.
Marlins right-hander Josh Johnson was called up from Double-A Carolina in 2005. He pitched well in relief, and also once filled the rotation spot of A.J. Burnett, who was kicked off the team for his conduct.
Josh Beckett started four games in late 2001 for the Marlins, posting four quality starts with a 1.50 ERA.
Reds first baseman Joey Votto first flashed his potential as a September callup in 2007, producing a .321/.360/.548 slash line in 24 games. He finished second in the National League Rookie of the Year voting the following year.
Other players can provide a memorable month. Minnesota's Michael Ryan is one of these. Although he wasn't a classic September callup in 2003 -- appearing in 10 games for Twins in August -- he certainly deserves mention. Ryan hit .404 with five home runs and 12 RBIs in 17 September games.
Who might be some of this year's key September callups? Well, the big-named prospects are probably off the table.
Orioles manager Buck Showalter all but ruled out right-hander Dylan Bundy joining the big club this year, saying the youngster needed to continue to progress.
Cardinals right-handed prospect Shelby Miller has a better chance than Bundy to be a late-season addition, though General manager John Mozeliak said it's unlikely a player not on the current 40-man roster -- like Miller -- would be added. There is a slight chance Miller could be used out of the bullpen, however. There is a precedent: Rays lefty David Price in 2008.
Royals fans have long been clamoring for outfielder Wil Myers -- and not just during the Futures Game in Kansas City. But the Royals likely will stick to their philosophy of not stripping Triple-A Omaha of its best players as the Storm Chasers prepare for the playoffs.
Rangers prospect Jurickson Profar is another top prospect fans would like to see. But with Elvis Andrus and Ian Kinsler manning the middle infield -- as well as, an albeit struggling, Michael Young -- Profar's impact likely would be minimal.
"We talked about a lot of guys," Rangers general manager Jon Daniels said last week. "We still have another week. Nothing is set in stone. Just like every other team is doing now, we're discussing our options."
There are plenty of options for clubs once expanded rosters become available. Some top prospects -- like Votto, Johnson and Beckett did -- might get their chance to shine. Others players -- like Chambers and Ford -- might greatly impact the pennant race.
And then there's always the possibility of someone joining Rodriguez as one of September's biggest callup stars.