The two moves opened up roster spots for relievers Joakim Soria, who was acquired in a Thursday deal from Detroit, and left-hander Bobby LaFromboise, recalled from Triple-A Indianapolis.
These were just pit stops on the Pittsburgh roster's conveyor belt. Two more moves will have to be made when left-hander A.J. Happ and first baseman/outfielder Michael Morse -- acquired in Friday Deadline deals -- check in.
Burnett and Guerra had combined to allow 14 of the runs in Thursday's 15-5 loss to the Reds.
For Burnett, the 38-year-old recently basking in the first All-Star selection of his 17-year career, it was clear something was off since the midseason break. He allowed 10-plus hits in each of his three starts of the second half -- something he had never done even two straight times in his previous 422 career starts.
LaFromboise, who spent a brief four-day stint earlier this season with the Pirates, put up a 2.72 ERA in 42 appearances with Indianapolis. He comes up in the midst of a hot streak, having allowed only one earned run in his past 17 outings, none in the past seven.
Tom Singer is a reporter for MLB.com and writes an MLBlog Change for a Nickel. He can also be found on Twitter @Tom_Singer and on his podcast. This story was not subject to the approval of Major League Baseball or its clubs.