SAN FRANCISCO -- St. Louis Cardinals rookie Alex Reyes insisted it was fun just to be able to watch three games with playoff-type pressure Thursday through Saturday against the San Francisco Giants.

But when the 22-year-old got his chance to stand on the hill in front of 41,000 people Sunday, he was able to treat it like just another game.

Reyes showed jitters only on an errant throw to first base, combining with two relievers on a five-hitter that led the Cardinals to a 3-0 victory over the Giants and a split of their four-game series.

"Playoff atmosphere ... it's amazing," the right-hander gushed after his seven-inning effort. "It was exciting just to be here."

Aledmys Diaz smacked a two-run home run off Giants starter Albert Suarez in the third inning, giving St. Louis a lead it would not relinquish en route to its second straight victory.

As a result, the Giants (79-70) and Cardinals (78-71) ended the series exactly where they started - with San Francisco holding a one-game advantage in the National League wild-card race with now 13 games to play.

Even after the narrow defeat, Giants manager Bruce Bochy was still trying to shake off Saturday's blown ninth-inning lead with a chance to sweep the first three games of the series.

"That's a big swing," Bochy said. "It's a fight from here on out."

The difference in the wild-card race now is that the New York Mets (80-69), who swept a three-game interleague series from the Minnesota Twins, have moved into the top wild-card spot ahead of the Giants.

Also, by winning the season series 4-3, the Cardinals would host a one-game tie-breaker should San Francisco and St. Louis finish the regular season deadlocked for the second wild-card spot.

"Biggest win of the year," Cardinals manager Mike Matheny said with a smile. "Can't wait for (Monday), because that could be the biggest win of the year. That's the way we approach it."

Making just his third career start, Reyes (3-1) dominated the Giants, allowing only four hits -- all singles -- in seven innings. He walked two and struck out six.

San Francisco's biggest threat against Reyes was created in part by a throwing error by the pitcher.

With Denard Span on first base and one out in the sixth inning, Reyes fielded a slow roller by Brandon Crawford and, despite hearing catcher Yadier Molina tell him to hold onto the ball, he threw wildly to first base. The error allowed Span to reach third base and Crawford second.

But with the potential tying runs in scoring position, Reyes struck out Hunter Pence and, after walking Brandon Belt, got Eduardo Nunez to fly to left field.

"He just has a presence on the mound. A confidence," Matheny said of Reyes. "That's something you can't really teach."

Even though the Giants got just five hits in the game, they advanced four baserunners into scoring position and stranded them all.

"We created some chances today; we just couldn't get them in," Bochy said. "We couldn't get the big hit."

Left-hander Kevin Siegrist pitched a one-hit eighth inning, and closer Seung Hwan Oh, the winning pitcher Saturday night in a two-inning stint, worked a 1-2-3 ninth for his 18th save.

Diaz's homer came on the first pitch after Matt Carpenter had lashed a two-out double into the right field corner in a scoreless game in the third inning.

The homer was his 16th of the season and gave his young pitcher some early breathing room.

"AD is a great hitter," Reyes praised. "That got the momentum for us."

Suarez (3-4) was pulled after five innings, having allowed two runs on five hits. He walked one and struck out two.

"Another good outing. One mistake," Bochy said. "He gives us a chance. We couldn't get him any runs."

The Cardinals added an insurance run against the San Francisco bullpen in the eighth.

Kolten Wong led off the inning with a triple off the third Giants' pitcher, left-hander Josh Osich. Pinch-hitter Jhonny Peralta followed with an RBI single off right-hander George Kontos.

Diaz and Molina had two hits each for the Cardinals, who improved their best-in-baseball road record to 45-30.

Nunez had two hits for the Giants, who completed a 2-5 homestand.

NOTES: RHP Alex Reyes lowered his ERA in three career starts to 1.53. ... The win was the Cardinals' 10th in their last 15 games against the Giants. ... The Giants were shut out for the 12th time this season. ... Home plate umpire Brian O'Nora had to leave the game in the second inning after getting hit in the face mask by a foul tip off the bat of Giants RF Hunter Pence, O'Nora was diagnosed with a concussion and will not be allowed to travel until passes Major League Baseball's concussion protocol. ... With a three-game road series against the Los Angeles Dodgers beginning Monday night, Bochy chose to rest C Buster Posey on Sunday. ... Giants LHP Madison Bumgarner is scheduled to duel Dodgers LHP Clayton Kershaw in the opener of the Giants-Dodgers series Monday night. ... The Cardinals will send RHP Carlos Martinez to the mound in the opener of their three-game road series against the Colorado Rockies on Monday night.