That will change on Sunday when he takes the hill against the Royals in the series finale at Kauffman Stadium.
"We saw him in Spring Training," Twins manager Ron Gardenhire said. "[He has a] live fastball. The ball jumps out of his hand. The breaking ball is OK, average.
"We haven't seen him as a starter, though. We were using him out of the bullpen [in Spring Training]. But he stretched out and stepped up, and he threw the ball great as a starter down there. So that's kind of exciting, because we kind of viewed him as a reliever out of Spring Training."
The Twins picked up Vasquez on waivers in November. He pitched the previous eight seasons in the Diamondbacks' organization, going 5-10 with a 4.66 ERA over the last three years.
With both teams essentially out of the postseason race, players like Vasquez and Mendoza have one month to state their case for a spot in next season's rotations.
"We're excited to see him," Gardenhire said of Vasquez. "I'm anxious to see how his breaking ball is. I've only watched him on TV, and TV throws a little deception at you as far as how they're breaking and what kind of snap it has on it. I'm anxious to see him get out on the mound. It'll be kind of fun."
Twins: Walters returns from 60-day DL
The Twins reinstated right-hander P.J. Walters from the 60-day disabled list on Saturday. Walters, who is 2-2 with a 5.40 ERA in seven starts with Minnesota this season, was placed on the DL with right shoulder inflammation on June 14.
Gardenhire said Walters could be used in a starting rotation that could swell to six or seven hurlers.
"We'd like to start [Walters]," Gardenhire said. "That's what he was doing before. That's what he's used to. We'll figure all that out, go with a six-man rotation, seven, whatever. That's what we'll do, but first we'll talk to the pitchers and let them know where we're at."
Royals: Lough hits leadoff in debut
Outfielder David Lough, called up by Kansas City on Saturday, batted in the leadoff spot and started in right field in the second game of the twin bill. He also logged his first two Major League hits.
"It's been a long ride, but I'm just happy to be up here," said Lough, who went 2-for-5 in his debut. "It's a slow process for some guys and I know I needed to work on some things. [The team] took it slow with me, and I don't feel like I should've been here years ago or anything like that. But I'm ecstatic, I really am."
The Kansas City media voted right-hander Jeremy Guthrie as the Royals' Pitcher of the Month for August after he went 3-1 in six starts. Left fielder Alex Gordon was the club's Player of the Month, after batting .310 with five homers.
The Royals' 17-11 record in August was their best for the month since posting an 18-11 mark in 1991.