Lake entered Wednesday's game with 12 hits in his first five games, and then doubled in his first at-bat in the first against the Diamondbacks. He joins George Kelly (1930) and Emil Verban (1948) as the only Cubs to have a dozen hits in their first five games.
He was promoted from Triple-A Iowa after Brian Bogusevic aggravated his left hamstring, which left the Cubs thin as far as outfielders. The club could've sent Lake back to the Minor Leagues after David DeJesus was activated from the disabled list on Wednesday, but instead, Dave Sappelt was optioned to Iowa.
Lake isn't going anywhere now.
"He's got that incredible physical ability, amazing tools, where when he is locked in and seeing the ball well, he can do some things on the baseball field that make you drop your jaw," Epstein said. "His development is all about maturation and the mental side of the game. He's made huge improvements in seeing the right-handed breaking ball. He used to be a really big chaser. It's something he's cut down on. ... You don't see guys with bodies like that and power and speed.
"He's got the physical abilities to take a big step forward. Do I think one week in the big leagues show that he has? No. We're really excited for him and the start he's off to."
Lake finished third in the Most Valuable Player Award voting in the Dominican Winter League, which Epstein said may have helped the rookie's confidence. David Jauss, whom Epstein knows from his days with the Red Sox, was Lake's manager in the Dominican Republic.
"He's showing right now he's playing with a ton of confidence that he really belongs here," Epstein said. "This is the league he feels he's ready for and he's going out and showing it."
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.