But Parker's 48th pitch of the day turned out to be his last. He fell in a heap in the midst of his attempt at retiring Allen Craig to end the inning, climbing to his knees for a few seconds before clutching his right hamstring.
The A's second-year starter tried to stay in the game, tossing a handful of warm-up pitches with manager Bob Melvin observing feet away. Oakland's skipper turned to Jesse Chavez in relief for what can either be interpreted as a best-case scenario due to precautionary measures or, through a more dire reading, Parker's inability to regain his form.
The report from Melvin after the game pegged "right hamstring tightness" as the cause of his early exit.
"It's semantics, to an extent," Melvin said. "Every cramp is a slight strain, based on hydration. We're hoping that's what it is."
Parker said he hadn't felt any discomfort prior to the incident and that he's never experienced anything comparable in his career. His preparation before the game mirrored that of every game this season.
"It was just something where I threw the pitch and it got tight on me," Parker said. "It happened so fast, I can't really tell you what happened. It's something we'll figure out in the next few days."
Parker offered little protest to remain in the game, adding later in the locker room that "it probably wouldn't have been the smartest thing to try to gut through and stay there.
"We made a good decision."
Cardinals ace Adam Wainwright lived up to his end of the bargain as he went the distance for his 11th victory, but the potential loss of Parker is a dispiriting blow to an Oakland starting rotation that entered the game 20-6 with a 2.98 ERA and .224 opponents' batting average over the last 39 games after a rocky start to the season.
Parker, a microcosm of Oakland's starting pitching success, was 4-0 with a 2.34 ERA and .176 opponents' batting average over his last six starts after beginning the year 1-5 with a 7.34 ERA and .345 opponents' batting average.
"It sucks, you know," Parker said. "I've just been building on outings prior and today everything was working good early and I was able to establish my fastball in and out. It's unfortunate."
Parker's outing followed A.J. Griffin's first shutout and Bartolo Colon's eighth straight win, a trend Chavez couldn't continue. Chavez allowed four earned runs in the subsequent 1 1/3 innings before Jerry Blevins replaced him in the sixth and promptly allowed a three-run home run to Matt Adams to break open the game, 6-0. Oakland's bullpen pitched 5 1/3 innings Saturday after accounting for just one inning in the two games prior.
"I'd like to say it was just one of those days," Chavez said. "I still have to do my job and I got to go deeper and save the bullpen so we don't have to use as many arms as we did today."
Wainwright, meanwhile, continued his dominance despite Parker's absence. Like Parker, Wainwright didn't allow a hit until late in the third inning. St. Louis' right-hander responded with his fourth complete game of the season to avoid losing a third straight start for just the fourth time in his career.
Oakland's lone run came on an RBI single by Josh Reddick in the eighth that scored Josh Donaldson from second. Donaldson was the A's first runner in scoring position all game.
"Every time, it seemed, we got a guy on first base, we hit into a double play," Donaldson said. "He's not going to be a guy to overpower you, but he's a very intelligent pitcher."
Of the five hits Wainwright allowed, two were off the bat of Derek Norris, who entered the game wallowing in a 4-for-39 slump over his previous 13 games. His single into left field in the third inning was his first hit since June 11.
Though the A's found productivity through an unfamiliar source, the team's more reliable staple -- bases on balls -- was nonexistent Saturday, in large part due to Wainwright.
Oakland, the most walked team in baseball, struck out eight times and reached base just twice via walks all game against Wainwright, whose 9.5 strikeout-to-walk ratio is the best in the Majors by a wide margin. Wainwright has walked just 12 batters through 125 2/3 innings this season.
"I read something today that the A's had swept five out of the last six home series," Wainwright said. "I text Yadier [Molina] and said, 'They're not sweeping us.' That's a great team over there. The lineup is very deep with a lot of guys that can hurt you and a quality pitching staff. We knew we had our work cut out for us."
Both starting pitchers brought it Sunday. Parker's early exit changed the course of the game completely.
"If he could've stayed in the entire game, we could still be playing 0-0," Donaldson said. "He really looked sharp early on. That's probably the best I've seen him all year."