Cosart has been as consistent a starter the woeful Astros have had this year, throwing at least five innings in all but one of his starts. However, he's allowed 14 earned runs in 15 2/3 innings in his last three outings and is 9-6 on the year with a 4.23 ERA.
The 24-year-old righty, who has never faced the Marlins, did not get a decision on Sunday in Chicago, as the White Sox reached him for four runs (3 earned) and seven hits in five innings of his team's 11-7 win.
"I was hoping to go six or seven even after the first; just come out and have some quick innings," Cosart said. "But it's baseball. I got a lot of ground balls. Obviously I didn't get the results and didn't go as long as I wanted to, but I thought I made some good adjustments to start the second half that I can only build off of and get better."
With a win on Saturday Cosart would become the first Astros pitcher to 10 wins since Lucas Harrell won 11 in 2012. No one on the staff had more than seven victories a season ago.
Houston is 11-8 in his starts this season.
Miami, meanwhile, will counter with righty Tom Koehler, who will be trying for his first win since July 2. Koehler did not get a decision on Monday in Atlanta, but pitched well, surrendering one run and five hits in 6 2/3 innings of a 3-1 win.
He is 6-7 overall on the year with a 3.85 ERA.
In Friday's opener, Jeff Mathis stroked a two-run double during the seventh inning and Brad Hand tossed 7 1/3 effective innings as Miami topped the Astros, 2-0. Donovan Solano and Giancarlo Stanton both supplied two hits for the Marlins, who have won five of their last six games.
Hand (2-2) allowed just three hits and two walks with four strikeouts to earn his second straight victory.
"That was a tremendous effort by Brad tonight," Marlins manager Mike Redmond said. "He was pounding the strike zone and was in complete control of the game."
Jose Altuve, Jason Castro and Gregorio Petit accounted for the Astros' three hits and starter Dallas Keuchel (9-7) gave up just two unearned runs on nine hits with no walks and seven strikeouts in Houston's third straight defeat.
"I don't think I lost it. I just think there were some bad breaks," said Keuchel. "I think I've been pitching well. It's just that the results haven't been there."
This is the first series between the teams since 2012, when Houston was still a member of the National League.