The Cubs' top prospect in the organization, Rizzo was batting .342 at Triple-A Iowa and leading the Pacific Coast League with 23 home runs when he got the promotion. He was in the starting lineup at first base and hitting third for the Cubs, who were set to face the Mets at Wrigley Field.
Manager Dale Sveum said that Rizzo will take over as the everyday first baseman, replacing Bryan LaHair.
"When you bring somebody up like that, there has to be some protection," Sveum said. "I think the three or four spot is legitimate, so somebody can hit behind him."
Said Alfonso Soriano: "I'd like to see him hit behind me."
"He's got to understand he's not the savior of this offense now," Sveum said Monday of Rizzo. "That's what he has to be careful of, is that he comes up here and tries to save a struggling offense. He can't do it with one swing of the bat all the time -- [although] it'd be nice if he does."
The first baseman started for Iowa on Monday against Round Rock in Des Moines, but was pulled in the fourth inning.
"I had no idea before the game," Rizzo said to reporters after Monday's game. "After that at-bat, I figured something was up because [Iowa manager Dave Bialas] usually comes out to get the helmet of whoever makes the final out.
"He didn't do it that time. He told me to come on in. That's when he told me I was going to Chicago."
This month, Rizzo is hitting .316 with six homers and 16 RBIs. Only Soriano has matched those numbers for the Cubs in June, hitting seven homers with 16 RBIs.
"I want to tell [Cubs fans] that there's going to be good times, and there will there be bad times," Rizzo said. "Hopefully there will be times I'm a hero, and there will be times that I'm the villain. That's the nature of the game, and that goes for every baseball player."
Sveum has kept an eye on Rizzo, 22, since February, beginning in Mesa, Ariz., at Spring Training and continuing as the Minor League season progressed. Sveum didn't check Rizzo's at-bats on Monday.
"I've seen plenty," Sveum said.
Last year, Rizzo was batting .365 at Triple-A Tucson when he was promoted to the Padres, and he struggled, batting .143 in 35 games. He was sent back to the Minor Leagues. When recalled in September, he batted .133 in 14 games. Jed Hoyer, the Padres general manager at that time, blamed himself, saying Rizzo still needed to develop.
Hoyer is now with the Cubs, as is Rizzo, whom the team acquired in January from San Diego for Andrew Cashner in a four-player swap.
Theo Epstein, Cubs president of baseball operations, has tried to keep expectations in check.
"You have to look at what happened last year," Epstein said last week. "[Rizzo] had great numbers and was rushed a little bit and came up and struggled, so it's important to put players in position to succeed, and always put your Major League club in position to succeed. ... Those things you don't want to rush into, there's more to development than numbers."
Coaches and scouts who have watched the first baseman at Iowa this year say he's developed an impressive pregame routine for both his hitting and defense.
Sveum will talk to Rizzo once he arrives.
"The conversation will be more the vanilla 'Get here and relax, don't try to carry the team on your shoulders by no means,'" Sveum said. "'That's not what you're here for -- you're here for the long-term future to make this organization and lineup much much better.'"
In a corresponding move Tuesday, infielder Adrian Cardenas was sent down to Iowa, where he was Rizzo's teammate earlier this season.
"He's dealt with cancer and that is a positive for him as far as baseball goes," Cardenas said of Rizzo, who was diagnosed with limited state classical Hodgkins lymphoma in late April 2008. "You deal with so much adversity as a baseball player and so many ups and downs, for him I think he can handle it.
"This is what he loves to do -- he enjoys baseball so much," Cardenas said of Rizzo. "I feel he's obviously not [Tony] Campana fast, but [Rizzo] plays with the same intensity. You won't see him jog on a groundball, you won't see him not dive, whether we're losing or winning by a bunch of runs. He does a good job of taking the small things into consideration and making the most of his opportunities."
The biggest question is, is Rizzo ready?
"Absolutely," Cardenas said. "He's more than ready. You guys are in for a treat."
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter@CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.