Volquez (15-5) walked four and struck out four in a 97-pitch effort. After a relatively rough stretch following the All-Star break, Volquez appears to be back on track.
"Nobody goes the whole year without scuffling," said Reds manager Dusty Baker. "Everybody was worried about him, saying he was tired. He's caught his second wind."
The Reds got to Cardinals starter Kyle Lohse early. Jay Bruce's RBI single put the Reds ahead, 1-0, in the first inning. St. Louis was unable to complete a double play on Javier Valentin's slow roller, allowing Jerry Hairston Jr. to score Cincinnati's second run.
Lohse (13-6) allowed three earned runs on seven hits in six innings. He walked three and struck out two.
Volquez was masterful early on. The Cardinals did not hit the ball out of the infield in the first three innings.
Volquez walked Ryan Ludwick with one out in the second, but Albert Pujols grounded into a 6-4-3 double play to end the inning.
Volquez needed just 39 pitches to get through four innings.
"His pitch count was relatively low," said Baker. "That was huge for us. If he can do that, he's going to go deep into ballgames."
Rick Ankiel's broken-bat pop fly to Bruce in right field leading off the fifth was the first ball to exit the infield, while Adam Kennedy's single to center with one out in the fifth was the Cardinals' first hit.
Things got a bit testy later in the fifth. After Volquez brushed back Lohse in the top of the inning, Lohse returned the favor, sending Volquez to his knees with a pitch in the bottom of the frame.
Both benches were warned by home-plate umpire Greg Gibson.
Volquez, who had just one strikeout through five innings, said he's trying to evolve into more of a ground-ball pitcher.
"I was struggling a little bit last month," Volquez said. "Sometimes I try to strike guys out too much. I'm a sinkerball guy now, a ground-ball guy."
When he needed a strikeout, however, Volquez was more than willing to appease. In the sixth, for example, consecutive one-out singles by Skip Schumaker and Ludwick put runners at first and second, and Pujols walked to load the bases.
The situation prompted a visit to the mound by pitching coach Dick Pole.
"He told me Ankiel was going to be swinging at the first pitch," Volquez said. "I went to my changeup on Pujols. I didn't want to get into trouble with him."
Volquez fanned Ankiel and Troy Glaus to end the inning.
"That was one of the finest pitching performances under pressure I've seen in a long time," said Baker.
The Reds went ahead, 3-0, on Jeff Keppinger's single to center that scored Edwin Encarnacion from second base.
Brandon Phillips launched his 20th home run, a three-run shot on an 0-1 pitch from Jaime Garcia, with one out in the seventh, to make the score 6-0. Phillips, who went 2-for-5, hit a homer in back-to-back games for the first time this season.
After the Cardinals scored their first run on Glaus' two-out RBI single off David Weathers in the eighth, Joey Votto's pinch-hit single scored Corey Patterson to make the score 7-1.
The Cardinals roughed up Francisco Cordero for two runs on four hits in the ninth.
Rookie outfielder Chris Dickerson, who went 3-for-5 with a double and a run scored, is hitting .409 through five big league games.
Baker was pleased to see his club respond after losing the first two games of the series to the Cardinals, especially with a nine-game, 11-day road trip upcoming.
"I want to see a team that competes," Baker said. "I don't care who you're playing or how many people are in the stands. I'm just glad that our young players are playing hard."