Going on the 15-day disabled list, as expected, were right-handers Charlie Morton (recovering from labrum surgery) and Brandon Cumpton (Tommy John surgery), catcher Chris Stewart (strained right hamstring), infielder Justin Sellers (sore left heel) and outfielder Jaff Decker (strained left calf).
Morton's status potentially removed any bullpen roadblocks, since Vance Worley stepping into the rotation would have accommodated both Hughes and Pimentel.
But the Pirates chose to go a different route, designating Pimentel for assignment and recalling Scahill, who had been optioned to Triple-A Indianapolis after pitching to a 1.80 ERA in nine exhibition outings.
The Bucs also put Florimon on DFA status, clearing the last seat on their bench for the power-packed, lefty-hitting Lambo.
This is the eighth DL placement since 2009 for Morton, starting his eighth year in the Majors.
The Pirates held out hope that Morton would be ready to take his spot in the rotation for the start of the season. But he got progressively less effective as Spring Training went on -- ironic, in that getting comfortable with his delivery after the surgery was his main challenge.
He allowed one run in five innings in his first two outings -- then 15 runs in the last 12 innings -- ending with the rough outing in Philadelphia on Saturday.
Florimon made a strong late push for a spot. Renowned for his defense and valued for his speed, he opened eyes with unexpected offense, batting .270 with five extra-base hits, including two home runs.
Lambo provides far more punch off the bench, and plays positions Florimon does not -- corner outfield, and first base.
With the moves, the Bucs finalized the 25-man roster for the start of their 128th National League season, Monday at 4:10 p.m. ET against the Reds.
Tom Singer is a reporter for MLB.com and writes an MLBlog Change for a Nickel. Follow him on Twitter @Tom_Singer. This story was not subject to the approval of Major League Baseball or its clubs.