ST. LOUIS -- Can the St. Louis Cardinals afford to have two rookie pitchers in their starting rotation when the games become do-or-die? Can they afford not to? After all, it is the veterans who have gotten them into this touch-and-go spot.

As the Cardinals navigate the final three weeks, that decision could make or break their search for a sixth straight postseason appearance. The question was thrust awkwardly in their faces again during Tuesday’s 4-2 win over the Chicago Cubs.

Rookie Alex Reyes rescued the Cardinals from another rough start by Jaime Garcia and ensured that the Cubs won't celebrate their 2016 division title at Busch Stadium. That raised the question of whether Reyes should be allowed to rescue the Cardinals from one of the worst stretches of Garcia’s career.

“We’ll figure that out later,” Cardinals manager Mike Matheny said.

The short-term evidence is overwhelmingly in Reyes’ favor, as Matheny and general manager John Mozeliak no doubt huddle in the coming days to see which of the pitchers will start what could be a critical game Sunday in San Francisco. In his past six starts, Garcia has an 8.23 ERA and 1.79 WHIP. In 28 major league innings, Reyes has struck out 34 batters, has a 1.29 ERA and has given up just 16 hits.

But it isn't as simple as it seems, in part because of sample-size issues. Garcia had a career 3.31 ERA in seven seasons before this one. That’s borderline elite. What if Reyes loses touch with the strike zone, as he has done in stretches this season, including large chunks of Tuesday’s game? He pitched 4 1/3 scoreless innings after Matheny wasted little time yanking Garcia in the second inning, but Reyes walked nearly one-third of the batters he faced. Reyes was as dominant as usual but also, at times, as wild as the Cardinals feared he might be. He walked six batters and threw nearly as many balls (42) as strikes (43).

The first order of business will be determining if Garcia is healthy. His velocity has held surprisingly firm, but he has pitched more innings than in any other season since 2011, when he was 24. He acknowledged that he could be hitting a wall of either physical or mental exhaustion.

“I’m trying to figure out what’s going on, whether it’s push things a little more or back off. I’m doing everything that’s in my power to be the best I can for the team, and unfortunately, I’ve let my team down,” Garcia said. “I’ve been through tough times before, and I’m going to continue to do what I can to fight and be there for the team.”

Garcia is at the center of the storm at the moment, but he’s hardly alone in having gotten the Cardinals into this perilous spot, a half-game behind the New York Mets for the second wild card with only 18 games left. The Cardinals have three of the highest ERAs in the National League among qualified starters: Garcia is fourth with a 4.65 ERA, Mike Leake is fifth with a 4.60 ERA and Adam Wainwright is eighth with a 4.45 ERA.

Alex Reyes pitched 4 1/3 scoreless innings of relief to hold back the Cubs. Dilip Vishwanat/Getty Images

It's actually a wonder that the Cardinals are in as good of position as they are with those numbers following around three of the pitchers they were counting on this season.

Matheny insists he wouldn’t hesitate to use Reyes in trying situations over the final weeks. He considered using him as the closer until Seung Hwan Oh’s strained groin muscle heals, but he instead opted to go with Kevin Siegrist. Matheny brought Reyes into a bases-loaded mess to bail out Garcia, and Reyes struck out Kris Bryant with a 98 mph fastball.

“This kid came into a real tough situation, and he pitched lights-out,” Matheny said. “When he got in trouble, he had swing-and-miss stuff when he had to have swing-and-miss stuff.”

Brandon Moss swung and connected with a Jason Hammel fastball right down the middle and hit it into the right-field stands in the sixth inning to get Reyes his second career win. Hammel bent at the waist, clearly disgusted with the location of the pitch, both before and after Moss swung. Moss entered the game in a 1-for-41 slump, and many Cardinal fans were calling on Matheny to bench him, but sometimes patience is, in fact, the best policy in this bedeviling game.

Dexter Fowler homered to center field on Garcia’s fifth pitch of the game. After Garcia walked Fowler to load the bases in the second inning, nothing happened for quite some time, as if Matheny were debating what to do with his struggling starter. It took long enough that, by the time Matheny came off the top step, Garcia looked surprised to see him emerge. Nonetheless, Matheny slowly walked to the mound and took the ball from Garcia.

It seems reasonable to wonder whether fatigue, pain or both could be the culprits. Garcia’s career, improbably, has survived the big three of pitching injuries: shoulder surgery, elbow reconstruction and thoracic-outlet surgery.

Aledmys Diaz, in his first start after missing about six weeks because of a broken thumb, at least spared Garcia his fifth straight loss by hitting a two-run home run to left field in the second inning.