Peguero was in the lineup batting second and playing right field on Saturday.
"We saw in Spring Training with the energy that he brought, he improved on the hitting ability, he's shown the power, he's shown the defense," manager Jeff Banister said. "That was the best option for us."
Peguero hit .340 with five doubles and a homer in 47 Spring Training at-bats for Texas and was happy to see action immediately upon his arrival in Arlington.
"I'm not to here to be walking around, I'm here to play and to help the team," Peguero said. "I'm happy to have the opportunity to play and take advantage of it."
Peguero is up because Ryan Rua went on the 15-day disabled list Saturday after spraining his right ankle in the home opener Friday. Outfielder Shin-Soo Choo is also ailing, having left Friday's game with back spasms, but he said he is improving and he's considered day-to-day at this point.
Peguero took the 40-man roster spot of Derek Holland, who went on the 60-day DL Saturday after leaving Friday's start after just one inning with a strained shoulder muscle.
Edwards was available in the bullpen Saturday, and Pimentel is expected to join the club Sunday. Edwards had a 2.92 ERA and a .167 opponents' batting average in 10 Cactus League appearances.
"Kind of one of the shining stars of Spring Training," Banister said.
Edwards struck out 18 in 12 1/3 spring innings.
"I felt like I did well in spring and did what I needed to do," Edwards said. "Some of the things they told me to go work on in Triple-A, I thought it was going to be helpful. I didn't really see [starting the season at Round Rock] as a negative."
Pimentel, a potential rotation candidate in Holland's absence, replaced Lisalverto Bonilla on the 40-man as Bonilla went from the 15- to the 60-day DL with elbow troubles.
Banister said the Rangers liked Pimentel's "big power arm" and will use him as a multiple-inning reliever, at least initially. Pimentel was 2-1 with a 4.50 ERA in 42 innings for the Pirates over the past two seasons. He has never made a Major League start, but started 150 of his 159 Minor League appearances since 2007.
"Velocity, movement, at times he can show you a plus slider, a split change that he uses, a three-pitch mix," Banister said when asked about Pimentel's assets. "The fastball at any given time can top out at 96-97 … more than anything else, he's a big, right-handed arm."