The Cardinals' Matt Carpenter and the Reds' Todd Frazier are first and second in the balloting for third basemen, each with more than six million votes, while Bryant is third with 3,559,446 votes. Promoted to the big leagues on April 17, Bryant ranks 15th in the National League with 43 RBIs (second on the team to Rizzo's 44), and he is batting .273 with 10 homers, 13 doubles and two triples. The last Cubs rookie to be named to the All-Star team was Geovany Soto in 2008.
Rizzo, who has received 2,564,264 votes, trails the D-backs' Paul Goldschmidt, who has more than seven million votes. The Dodgers' Adrian Gonzalez was second among first basemen, followed by the Reds' Joey Votto and the Cardinals' Matt Adams.
Rizzo has posted impressive numbers this season, ranking fourth in the Major Leagues in OPS (.981) and third in the NL in on-base percentage (.413), sixth in slugging percentage (.568) and 10th in batting average (.304).
"He's definitely that anchor in the middle of the lineup who you want to build around," manager Joe Maddon said of Rizzo.
"To envision a lineup without him out there would be very difficult," Maddon added. "He hits righties, hits lefties, plays a really good first base, has been a really good baserunner. He's played a really complete game."
Giants catcher Buster Posey has received nearly eight million votes, while Montero, a two-time All-Star who was on the NL team last year, had 1,485,095 votes.
Castro, a three-time All-Star, had received 2,185,861 votes, and trailed the Cardinals' Jhonny Peralta, the Giants' Brandon Crawford and the Rockies' Troy Tulowitzki.
Fans can cast their votes for starters at MLB.com and all 30 club sites -- on their computers, tablets and smartphones -- using the 2015 Esurance MLB All-Star Game Ballot until Thursday at 10:59 p.m. CT. For the first time, voting is exclusively online, where fans may submit up to 35 ballots.
Fans may also receive the ballot by texting VOTE to 89269 (USA) or 101010 (Canada). Or text VOTA for a ballot in Spanish. Message and data rates may apply. Up to five messages. No purchase required. Reply STOP to cancel. Reply HELP for info.
The 2015 All-Star starters will be unveiled on Sunday at 6:30 p.m. CT on the Esurance All-Star Starters Selection Show on ESPN. Then on Monday at 6 p.m. CT, the All-Star reserves, pitchers and Final Vote candidates will be announced on the Esurance All-Star Selection Show on ESPN, immediately after which fans can return to MLB.com to begin casting their 2015 Esurance MLB All-Star Game Final Votes for the final player for each league's All-Star roster. Final Vote ends Friday, July 10, at 3 p.m. CT. On Tuesday, July 14, watch the 2015 All-Star Game live on FOX, and during the game visit MLB.com to submit your choice for the Ted Williams Most Valuable Player Award presented by Chevrolet via the 2015 MLB All-Star Game MVP Vote.
MLB.com will provide extensive online coverage of All-Star Week festivities.
The 86th All-Star Game will be televised nationally by FOX, in Canada by Rogers Sportsnet and RDS, and worldwide by partners in more than 200 countries via MLB International's independent feed. ESPN Radio and ESPN Radio Deportes will provide national radio coverage of the All-Star Game. MLB Network and SiriusXM will also provide comprehensive All-Star Week coverage. For more information, please visit allstargame.com.