Butler's work allowed the Rockies to rally from a seven-run deficit and eventually tie the game.
It wasn't bad for a pitcher who hadn't pitched in relief since his first pro outing in Rookie-level ball at Grand Junction in 2012 -- a planned piggy-back with another starter -- and had no real idea how to warm up to replace a struggling starter.
"I didn't even know how to approach it," said Butler, who threw 31 warmup pitches before bullpen coach Darren Holmes told him to save some for the game.
"Eddie Butler did a great job in a role that he's not accustomed to, coming in there, keeping the Pirates at seven [runs] and giving us a chance to fight our way back into it," Rockies manager Walt Weiss said.
Butler, 25, went 2-0 with a 4.09 ERA in four starts at Albuquerque, and he was originally scheduled to start there Wednesday night. He threw 41 pitches against the Pirates. Weiss said before the game that if Butler isn't overused in relief, he could step into De La Rosa's rotation spot Sunday at Arizona. Current Rockies long reliever Christian Bergman, who threw 51 pitches after replacing De La Rosa during Tuesday's loss to the Pirates, is another candidate for the Sunday start.
It's a new chance for Butler, a supplemental first-round pick in the 2012 Draft who may have been rushed a couple years ago.
Butler went 4-11 with a 6.04 ERA in 19 big league starts over the past two years, including 3-10 with a 5.90 ERA in 16 starts over two stints last season. Butler worked with his longtime pitching coach, former Major Leaguer Gary Lavelle, and rebuilt confidence in his sinking fastball, a pitch he lost after trying to develop a four-seam fastball at the Rockies' request.
Butler arrived at Spring Training with his sinker, but also with a slider and the ability to use the four-seamer and changeup. However, issues with two strikes or two outs cropped up, so he was sent to Albuquerque. After hard luck with ground balls in his first Triple-A start, Butler has gone six innings in each of his past three outings, with a 3.00 ERA, 10 strikeouts and three walks.
"I'm just pitching smarter and staying down in the zone and getting ahead of guys -- the things you need to do to have success," Butler said before his relief appearance. "That was the big thing, throwing lots more pitches in the zone for strikes."
• Righty Miguel Castro (1.50 ERA in six appearances), who hasn't pitched since April 17 because of a right shoulder strain, played catch Wednesday for the first time since the injury and reported feeling good.