Betts is also gaining on his teammate and friend Jackie Bradley Jr., closing within 225,000 votes of the center fielder for second on the ballot.
Of course, Betts and Bradley would love to be teammates in the starting lineup in San Diego on July 12.
"That would be pretty special," said Bradley earlier this week. "We've both worked really hard in order to help the team any way we can, and what better guy to deserve it than Markus? My very first roommate. You couldn't even script something like that. It would be pretty special if we do happen to make it. It would definitely be a unique situation."
Betts is hitting .287 with 99 hits, 18 doubles, four triples, 16 homers and 54 RBIs. Bradley, who had a 29-game hitting streak earlier this season, has a .294 average with 13 homers, 50 RBIs and a .950 OPS.
There is a strong chance that two other Red Sox players -- shortstop Xander Bogaerts and designated hitter David Ortiz -- will earn starting spots. Bogaerts and Ortiz have held wide margins at their respective positions throughout the voting.
Fans can cast their votes for starters at MLB.com and all 30 club sites -- on their computers, tablets and smartphones -- exclusively online using the 2016 Esurance MLB All-Star Game Ballot until tonight at 11:59 p.m. ET. Vote up to five times in any 24-hour period for a maximum of 35 times.
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Following the announcement of the 2016 All-Stars, be sure to return to MLB.com and cast your 2016 Esurance MLB All-Star Game Final Vote for the final player on each league's All-Star roster. On Tuesday, July 12, watch the 2016 All-Star Game presented by MasterCard 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 2016 MLB All-Star Game MVP Vote.
The 87th All-Star Game, in San Diego, will be televised nationally by FOX, in Canada by Rogers Sportsnet and RDS, and worldwide by partners in more than 160 countries via MLB International's independent feed. ESPN Radio and ESPN Radio Deportes will provide national radio coverage of the All-Star Game. MLB.com, MLB Network and SiriusXM will also provide comprehensive All-Star Week coverage. For more information, please visit allstargame.com.