San Diego has used 13 starters this season, and only Volquez and Clayton Richard have made all of their scheduled starts. Richard earned the win in Wednesday's 8-4 victory over the Astros, and Volquez will throw on Thursday in the final game of a four-game series at Petco Park.
Manager Bud Black knows that Volquez has been a reliable arm in the middle of the chaos of an ever-changing rotation.
"There is nothing more valuable to a team than a starting pitcher who makes every one of his starts," Black said.
Volquez has a 3.69 ERA but only sports a 5-7 record because he has received the lowest average run support in the Majors, at 2.72 runs per game.
The Padres look more likely to support him on Wednesday after scoring seven or more runs in four of their last five games. In July the Padres have averaged 4.64 runs per game after averaging 3.13 in April and 3.29 in May.
"The key to that now is to be able to sustain it. ... That's the thing you need to do ... put up some runs every night," Black said. "Our guys are capable of that."
Runs -- and wins -- haven't come easy for the Astros recently. They have lost 15 of their last 17 games overall and 15 of 16 on the road. They are 10-37 on the road this season.
"We want to make sure these guys continue to play hard, because when they continue to play hard, they're going to make a lot of mistakes," manager Brad Mills said. "If you're going to make mistakes, it's better to make them being aggressive than not being aggressive."
The Astros' four runs on Wednesday were an offensive outburst compared with their run production in five games since the All-Star break: 1, 2, 2, 2, 2.
The Astros are batting .215 since June 6.
Rookie Lucas Harrell, who will start for Houston on Thursday, has been fantastic at Minute Maid Park, posting a 5-1 record and 1.99 ERA. It's been a very different story on the road, where he is 2-5 with a 6.21 ERA heading into the series finale.
Batters are hitting .290/.351/.452 off Harrell away from Minute Maid Park, and .222/.283/.311 in Houston.
Harrell's only career appearance against the Padres was a good one, though. On June 27 he became the only rookie to throw a complete-game shutout this season, blanking San Diego at Minute Maid Park. He allowed six hits and struck out seven in that start.
Padres: Quentin back in the lineup
Outfielder Carlos Quentin went 1-for-3 with a walk in his return to the lineup on Wednesday after missing the previous two games with soreness in his left knee.
According to Black, Quentin tweaked the knee during Sunday's win over the Dodgers. Black wanted to be cautious and used the situation as a chance to give Quentin some time off during a long Major League season.
"I think the first day of Spring Training, you feel pretty good. Then after that it sort of slides. ... It's all downhill," Black joked.
Quentin is batting .268 with eight homers in 127 at-bats.
Outfielder Cameron Maybin was a late scratch from Wednesday's game with soreness in his right wrist. He is batting .368 over his last five games.
Astros: Rodriguez's streak ends
Wandy Rodriguez had lasted five or more innings in 48 straight starts before leaving after the fourth inning on Wednesday. He retired the first nine Padres in order before giving up five runs in the fourth.
Seventh-round pick Preston Tucker, an outfielder from the University of Florida, signed with the Astros on Wednesday. He was assigned to short-season Tri-City, where he was set to bat eighth as the designated hitter on Wednesday night.
With two homers on Wednesday, Matt Downs became just the second Astro with a multi-homer game this season. Chris Johnson hit two against the Mets on May 2.