Volquez is off to a slow start, with an 0-2 record and 4.30 ERA, and he has a lifetime 9.72 ERA against the Nationals.
The Nationals' 14-4 record after Wednesday's 7-2 victory over the Padres is the best in the National League, and they owe most of that success to their pitchers, since they have had to scuffle to generate runs.
"We've [had] to scratch and claw and try to get a couple of runs," Nationals manager Davey Johnson said before Wednesday's win. "We've got to be perfect with our pitching. Hopefully, we'll see some hitting in sight and our offense will pick up. It's been a rough start for runs."
The Nationals had won three in a row while scoring a combined eight runs before the offense broke loose in Wednesday's game.
Edwin Jackson will be on the hill trying to deliver Washington a sweep. The Nationals assured themselves of their sixth straight series win to begin the season with Wednesday's victory.
Jackson's last outing was the antithesis of his previous start, when he pitched a two-hitter against the Reds. On April 19, Jackson pitched five innings and allowed five runs on seven hits against Houston.
Padres: Guzman might play in finale
Padres left-fielder/first baseman Jesus Guzman might be ready to return to action Thursday after he had two teeth extracted and missed two games. Guzman is "feeling a little better," Padres manager Bud Black said Wednesday, and the right-handed hitter proved it by singling in a pinch-hit appearance.
Third baseman Chase Headley had a hit in four at-bats in Wednesday's game, and now has hit safely in 15 of the past 16 games.
Shortstop Andy Parrino had his five-game hitting streak snapped Wednesday.
Nationals: Some good news on Zimmerman
Third baseman Ryan Zimmerman remains sidelined with a sore right shoulder. Zimmerman had an MRI exam, and while it revealed no structural damage, he'll have to be pain free before returning to action.
"I think the important thing is there's nothing wrong with my shoulder," Zimmerman said. "That was good news, obviously. I don't think anyone thought there was going to be anything wrong, but I have proof that there's nothing wrong. I guess it's good peace of mind. Now it's just a matter of figuring out the right combination to get it to relax, and once that's done, I'll be ready to go."
The Padres are in the midst of a stretch in which they play 16 of 19 games and 21 of 29 through May 20 at home.
The best 18-game start for the Nationals since moving to D.C., prior to Wednesday, was 9-9, in 2005 and again in 2011.