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.
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.