With 337,473 votes, Betts holds a slight lead over Michael Brantley of the Indians (333,703) and teammate Andrew Benintendi (327,047).
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Xander Bogaerts is also making a bid to be an All-Star for the second straight season. The sweet-swinging shortstop ranks third at his position with 252,379 votes, trailing Francisco Lindor and Carlos Correa.
Betts finished second to Trout in the AL's Most Valuable Player Award race last year and is having another strong season. Entering action on Wednesday, Betts was slashing .276/.355/.495 with nine homers, 32 RBIs and eight stolen bases. He has also played excellent defense in right field.
When Betts was moved back to the leadoff spot earlier this month, he started heating up. The Red Sox have also started to regain their groove at the top of the order, with Betts setting the tone.
"I just think he's getting pitches in the middle of the plate and he's not missing," said Red Sox manager John Farrell. "We've seen for almost two years now when he gets in one of these runs, it's a lot of hard contact, impact to the baseball and extra-base hits are pretty frequent. And he's in that spot right now."
This is the first time Benintendi has been on the ballot. He has impressed the Red Sox and their opponents during his first full season.
"He's really good. I'm not afraid to say it, but that's Freddie Lynn reincarnated right there. That's a pretty good comp," said Cubs manager Joe Maddon after seeing Benintendi play for the first time earlier this season.
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 11:59 p.m. ET. 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.