"I am very thrilled to have the opportunity to go," Sanchez said before the start of Sunday's game against Texas at Rangers Ballpark.
"I am happy for him. He works hard, he is very deserving," Marlins manager Jack McKeon said.
The All-Star game is July 12 at Citizens Park in Phoenix.
Sanchez, 27, is in his second full season with the Marlins, and his hitting .292 with 13 home runs and 46 RBI.
Sanchez will be behind Fielder and the Reds' Joey Votto at first base. Fielder (.299, 21 home runs, 69 RBI) was voted in as starter by the fans, and Votto (.316, 12 home runs, 51 RBI) was the players' pick.
There were few surprises in Sunday's selections, though Bochy showed preference for his Giants pitchers, selecting three of his own players with three of the picks set aside for the manager, to give the Giants four of the 13 NL pitchers.That included Tim Lincecum, who is 6-6, and McKeon questioned that decision.
"Do we reward for what you are doing now or do we reward for what you have done in the past?" McKeon said.
On the American League side, the Yankees have the most All-Stars with four starters and two reserves, but many felt New York was still snubbed since C.C. Sabathia (11-4, 3.05 ERA), was passed over by AL manager Ron Washington.Washington, manager of the Rangers, also showed preference to his own players, picking C.J. Wilson (8-3, 3.14), who started Sunday's game against the Marlins, instead of Sabathia.
Sanchez is the lone Marlin on the team, the first time since 2007 that the Marlins have had just one player on the NL roster.
Sanchez, who grew up in Miami and played for the Hurricanes, was selected in the fourth round of the 2005 Major League draft by the Marlins.
Braun is one of three Brewers who will start for the National League, joining Fielder and second baseman Rickie Weeks.Sanchez had been hitting above .300 this season until June 28 and is on track to set personal highs in most offensive categories.