The Astros and Cardinals begin a three-game series Tuesday at Busch Stadium, then play another three games next week in Houston.
In between, the Astros play three games against the Pirates and later play three games against the Brewers, both of whom are still in the tight NL Wild Card race.
The Cardinals beat the Dodgers, 5-2, in 12 innings, Sunday to take a one-game lead over Los Angeles for the second Wild Card spot.
St. Louis is 2 1/2 games ahead of the Brewers and three games ahead of the Pirates.
The Astros just finished dealing a blow to the Phillies' playoff aspirations, taking three of four from Philly, including a 7-6 victory Sunday.
Fernando Abad, a promising but winless lefty, will start Tuesday for the Astros. Kyle Lohse, who has the best winning percentage (.824) in the Majors among starting pitchers, will get the call for the Cardinals.
Abad spent the first four months of the season in the Astros' bullpen and Triple-A Oklahoma City before being converted into a starter.
In four starts in the Majors, Abad is 0-4 with a 6.89 ERA, though he put up good numbers as a starter in the Minor Leagues (15-11, 2.37 ERA). The Astros have yet to see that kind of success as a starter at the Major League level.
On Wednesday, Abad struggled once again in a 5-1 setback to the Cubs. He gave up one run and four hits in 3 1/3 innings, but struggled and constantly pitched from behind in the count.
"It was tough to watch him early," Astros manager Tony DeFrancesco said. "There were a lot of deep counts and he fell behind and didn't seem he could locate his fastball early, and it was time for him to come out of the game when the situation came."
The Astros are committed to Abad in the rotation for the time being as they employ a six-man rotation, but they would like to see progress.
"Abad is going to have to battle," DeFrancesco said. "We're trying to get him to make quality pitches and he's working hard in his bullpens and his sides and he's just got to bring it across the lines."
Lohse, who will be making his 31st start, is 14-3 with a 2.81 ERA, but he lost his last start even though he pitched well in a 3-2 loss to the Padres on Wednesday.
Lohse had an eight-game winning streak snapped despite a six-inning effort in which he struck out eight and gave up just two earned runs.
"He was sharp right from the beginning. Those are starts we need to capitalize on," Cardinals manager Mike Matheny said. "But certainly, he did what he could do."
One of those earned runs came when Padres second baseman Logan Forsythe homered in the second inning.
"That was a tough one," Lohse said of the outing. "I felt really good, made a mistake, gave up a home run, and the other ones, I felt they did a good job of hitting some decent pitches."
Astros: Martinez eager to play spoiler
Outfielder J.D. Martinez's attitude is typical of how his team is approaching the end of the season.
"That's really what we have fun with now," Martinez said. "We know we have no chance for the playoffs, and now we just want to have a good time and play spoiler and have fun while we do it."
Cardinals: Boggs expected back
Reliever Mitchell Boggs is expected to be available Tuesday after Monday's off-day.
Boggs had some lower back tightness during his appearance on Saturday and was not available Sunday.
This will be the Astros' last trip to St. Louis as a member of the NL. The Astros and Cardinals will play next year in St. Louis in a two-game Interleague series on July 9-10.
Tuesday's game begins a stretch of nine straight games against sub-.500 teams for the Cardinals. In addition to the six games against the Astros, they have three games remaining with the Cubs.