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7/10/2014 12:11 A.M. ET

Twice as nice: Mookie's speed on full display in rallies

Rookie notches infield double when he notices nobody is covering second base

BOSTON -- Mookie Betts reached base just five times in his first six games, so he hasn't gotten to showcase his speed, which he considers his best attribute.

On Wednesday night at Fenway Park, Betts made a heads-up play and took advantage of that speed to start an eighth inning rally in a 5-4 walk-off win over the White Sox.

He used his wheels to hit an infield double.

"I've actually done it a couple times in the Minor Leagues," said Betts, who is ranked Boston's No. 5 prospect, "but the Minor Leagues is different from here."

With the Red Sox trailing, 4-0, to start the eighth, Betts grounded a ball into the hole between short and third and beat the throw. White Sox second baseman Gordon Beckham went to back up first, and shortstop Alexei Ramirez wound up closer to third trying to make the play.

Betts realized there wouldn't be anyone at second as he crossed first base and took off for second.

"It was a big gamble, but [manager John] Farrell says be aggressive the same way I've been my whole career," Betts said. "I saw the second baseman going to back up and I know the shortstop had to come in on it. I knew second base had to have been open, and looked, and again just took a gamble and went."

Dustin Pedroia knocked in Betts to put Boston on the board, and then David Ortiz and Jonny Gomes followed with doubles to cut the White Sox lead to one.

In the ninth, Betts reached when Javy Guerra hit him with two strikes. Daniel Nava hit a double off the Green Monster and Betts flew around the basepaths to tie the game. He finished 2-for-3 with two doubles, the other two-bagger coming when he worked an 11-pitch at-bat off Chris Sale and ripped a ball off the Monster.

"I wish I was that fast," Nava said. "That would be nice. You obviously saw with that play beating out the infield hit and getting to second. ... I think we've been missing out on a lot of the speed this year, and it certainly came up big right there."

Official scorer Bob Ellis ruled it a double, because he didn't consider the White Sox not covering second a fielder's choice, and he had no other reason to not give Betts a two-bagger for the heads-up play.

"My assessment after the fact was that nobody was close enough to second base to deter him from running there," said White Sox catcher Tyler Flowers. "I was more caught up in the play and trying to read if I thought he was safe or out. I thought he was safe, to be honest with you."

Steven Petrella is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.