CHICAGO (AP) -- Even the Chicago White Sox relievers don't know who will get the ball in the ninth inning.
Zach Putnam has had the last two chances, and made the most of them.
Putnam earned his third save and second in two nights, striking out Jason Castro swinging to end the game with two on and give the White Sox a 4-3 victory over the Houston Astros on Saturday night.
''It's interesting, and there's definitely an element of fun to it,'' Putnam said. ''We don't know from game to game who is going to have that ninth if it's a save opportunity.''
The White Sox have had no steady closer after Nate Jones and Matt Lindstrom were injured, and Ronald Belisario struggled in the role.
They have been closing games by committee, and four relievers combined to throw three scoreless innings Saturday.
White Sox manager Robin Ventura turned to Putnam to record the final out after Jake Petricka allowed a walk and infield hit in the ninth.
''Unfortunately, I don't have a guy that you're just going to leave out there, saying that's your closer,'' Ventura said. ''I like Put's swing-and-missability with some lefties, and that's the reason.''
Tyler Flowers had three hits and drove in the go-ahead run in the fifth for the White Sox, who have won two straight against the Astros to open the second half.
George Springer hit his 20th home run, a solo shot, and Jose Altuve had a two-run double for the Astros.
Flowers' RBI double snapped a 3-all tie after Alejandro De Aza tripled. Flowers, who also drove in the go-ahead run with a double in the seventh of Friday's 3-2 victory, had his first three-hit game since April 24.
''I don't know where he went over the break, but you can come back with renewed energy,'' Ventura said. ''Catching's a tough thing to do. I think you don't find too many catchers that are going to hit all year long. It's a tough position, and people that do it are special. With him getting some rest, maybe it kind of gets him going in the right direction.''
Flowers is 6 for 9 in his last three games after going 10 for 112 in his previous 34.
''I don't know if I'm quite locked in yet,'' Flowers said. ''It's good to put some quality at-bats together.''
White Sox starter Hector Noesi (4-7) gave up three runs in six innings and has lowered his ERA from 11.74 to 5.21 since joining the rotation.
''I'm getting prepared for the second half to be tough,'' Noesi said.
''So, I'm more aggressive when I go to the mound.''
Dallas Keuchel (9-6) allowed four runs and 12 hits in five innings. He was 7-2 with a 3.13 ERA in his previous 10 road starts.
''When you look at the amount of trouble he was in, to minimize it to four runs - and only three were earned - he did a nice job of battling,'' Astros manager Bo Porter said.
The White Sox went ahead 1-0 in the second after three singles and an error.
Conor Gillaspie extended the lead to 2-0 with an RBI single in the third. Flowers was hit by a pitch with the bases loaded to bring in another run.
Springer's homer cut it to 3-1 in the fourth. He is one home run shy of tying Lance Berkman's club rookie home run record, set in 2000.
Altuve's double tied it at 3 in the fifth.
The game featured three challenged calls and replay reviews totaling 5 minutes, 39 seconds. All were overturned.
In the third, Gordon Beckham appeared to be hit by a pitch, loading the bases. The Astros challenged the call, and review confirmed Beckham was not hit. He returned to the plate and struck out.
In the fourth, the White Sox's Alexei Ramirez was called out on a grounder to third, but replay confirmed he was safe at first. Later in the inning, Jose Abreu was called safe at second on a fielder's choice. The Astros challenged the call, and Abreu was ruled out.
NOTES: The White Sox optioned INF Carlos Sanchez to Triple-A Charlotte and will make a corresponding move on Sunday. .Abreu, who was leading the majors with 29 homers, is expected to play far more games than he did in Cuba, where he said teams play 96 games. He said he doesn't expect fatigue to be an issue. Ventura noted Abreu can sometimes DH to allow for rest.