"We realized David wasn't coming back as early as he might have hoped and we might have hoped," Alderson said.
Herrera provides the Mets much needed athleticism up the middle and is expected to take pressure off his new double-play partner, Wilmer Flores. Shifting Murphy to the corner regulates Eric Campbell to a bench role. Herrera was hitting .370 with 18 runs scored and 11 RBIs in 20 games for Triple-A Las Vegas this year. Herrera has experience at shortstop and third base in the Minors, but played second base exclusively this season.
"He's going to play second base," manager Terry Collins said of the Mets' No. 6 prospect. "That's where he's been playing, where he's comfortable playing. He's got enough on his plate coming up here in this particular situation. I think I'll leave him alone."
The Mets recalled the 21-year-old Herrera from Las Vegas late Thursday night after dropping their third straight game. They have lost five of seven since an 11-game winning streak, due in large part to continuously sloppy play from the middle infield. Flores now has six errors -- already more than he committed in 51 games at shortstop in 2014 -- with Murphy adding four of his own.
"We wanted to change things up a little bit," said Alderson, who denied Herrera was a candidate for promotion before Thursday's game and recalled him immediately after. "I think this is the realization that we need to introduce another option."
Meanwhile, both Alderson and Collins reiterated that Flores' job at shortstop is safe.
"We know he can catch the ball," Alderson said. "The important thing right now is that he understands we have confidence in his ability to catch the ball. He's demonstrated it. This is not a hope and a prayer."
Murphy has played 44 career games at third, including 16 last season. He's been the Mets' primary second baseman since 2012 and was the team's lone All-Star representative in 2014 thanks in large part to his bat, which is starting to heat up. Campbell struggled after a fast start filling in for Wright and is hitting .204 overall. He was never viewed as a long-term option at the position.
New York optioned left-handed reliever Jack Leathersich to Triple-A to make room for Herrera, who hit .220 in 59 at-bats as a late-season callup in 2014. The Mets are now carrying 13 position players for the first time since camp broke after playing the entire month of April with an extra pitcher.
Joe Trezza is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.