Alonso entered the day with 14 home runs, including 10 in the month of May. His previous career high for a season was nine, set in 2012 with the Padres. Alonso is hitting .290 overall, with a .388 on-base percentage and a .664 slugging mark for a 1.052 OPS.
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The 30-year-old infielder has received 287,975 votes. Cabrera, an 11-time All-Star, leads the way with 326,952 votes.
"Well-deserved," A's manager Bob Melvin said. "I haven't looked at all the numbers, but there are some pretty good names as far as first basemen go. But for a guy that hasn't really been in that position before, to be second right now is a nice little feather in his cap. If you do look at the overall numbers, he deserves to be there."
Cleveland's Carlos Santana narrowly trails Alonso with 270,816 votes, with Kansas City's Eric Hosmer (225,989) and Houston's Yuli Gurriel (182,945) also landing among the top-five vote-getters.
Miami, the site of this year's All-Star Game, is where Alonso has made his home since age 11, when he defected with his family from Cuba. He attended the University of Miami and returns to the city each offseason.
Fans may cast votes for starters at MLB.com and all 30 club sites -- on computers, tablets and smartphones -- exclusively online using the 2017 Esurance MLB All-Star Game Ballot until Thursday, June 29, at 8:59 p.m. PT. On smartphones and tablets, fans can also access the ballot via the MLB.com At Bat and MLB.com Ballpark mobile apps. Vote up to five times in any 24-hour period for a maximum of 35 ballots cast.
Following the announcement of the 2017 All-Star starters, reserves and pitchers, fans should return to MLB.com and cast their 2017 Esurance MLB All-Star Game Final Vote for the final player on each league's All-Star roster. Then on Tuesday, July 11, while watching the 2017 All-Star Game presented by MasterCard live on FOX, fans may visit MLB.com to submit their choices for the Ted Williams Most Valuable Player Award presented by Chevrolet with the 2017 MLB All-Star Game MVP Vote.
The 88th Midsummer Classic, at Marlins Park in Miami, will be televised nationally by FOX Sports; in Canada by Rogers Sportsnet and RDS; and worldwide by partners in more than 160 countries. ESPN Radio and ESPN Radio Deportes will provide exclusive national radio coverage, while MLB Network, MLB.com and SiriusXM will have comprehensive All-Star Week coverage. For more information about MLB All-Star Week and to purchase tickets, please visit AllStarGame.com and follow @AllStarGame on social media.