The roster moves the Cubs anticipated making Saturday had to wait a day.
But the organization stuck with the same plan Sunday morning, activating Jason Heyward off the disabled list and calling up right-handed pitcher Dylan Floro.
In return, Tommy La Stella and Pierce Johnson were sent down to Triple-A Iowa.
Heyward hit the DL earlier this month with a finger injury and played one game of rehab Thursday night with Class-A South Bend, collecting an RBI single in three at-bats.
Heyward entered play Sunday hitting .253 with a .697 OPS and was immediately in the lineup for the series finale against the Milwaukee Brewers, hitting sixth and playing right field.
Johnson made his MLB debut Friday before - and after - the two-hour rain delay. He allowed two unearned runs on two hits and a walk, striking out a pair of batters in his one inning.
Floro, 26, made one appearance for the Cubs earlier in the month, throwing 4.1 innings and allowing just one run.
La Stella, meanwhile, is the victim of a numbers game, getting sent down to the minor leagues for the second time this season.
The 28-year-old infielder is hitting .304 with a 1.006 OPS at the big league level including an 8:2 walk to strikeout ratio, but the Cubs opted to keep top prospect Ian Happ in the big leagues for at least a little while longer, making La Stella expendable.