Lopez, a Generation Adidas signing, was picked in the first round of the 2013 draft by MLS Cup champion Sporting KC. He made his debut last season in the U.S. Open Cup, and also participated in all three matches for the U.S. team at the Under-20 World Cup.
Kempin will be spending his second straight year in the USL PRO league, and will be coached on the new Oklahoma City club by former Sporting KC goalkeeper Jimmy Nielsen. Duke also returns to the USL PRO level after spending last season with Orlando City.
All three players can be recalled by Sporting KC at any time.