SAN FRANCISCO -- The St. Louis Cardinals won a game they needed to win, and the San Francisco Giants left the field shaking their heads.

Welcome to the 2017 baseball season.

Randal Grichuk gave St. Louis the lead for good with a second-inning home run, and Tommy Pham drove in a pair of late insurance runs, helping the Cardinals defeat the Giants 5-2 Thursday night in the opener of a four-game series.

St. Louis starter Michael Wacha (10-7) limited the struggling Giants to one run in six innings to snap a personal three-game losing streak. The right-hander combined with five relievers on a seven-hitter.

"Just a blip; he's been good all year," Cardinals manager Mike Matheny said of Wacha's losing streak. "You have a couple of games where the results aren't there but the stuff looks right. Don't put too much stock in that because everybody goes through that during the season."

The Cardinals (67-66) gained a half-game on the idle Colorado Rockies (72-61) in the National League wild-card race, trimming their deficit to five games.

It was an all-around bad night for the Giants, who began the game by scratching scheduled starter Madison Bumgarner because of an illness and ended it seeing Brandon Crawford have an apparent home run overturned by a video review.

"They're saying it was fan interference. They're wrong," Giants manager Bruce Bochy said minutes after getting an explanation from the umpires. "Terrible overturn there. Shocked all of us. It's a home run taken away from Craw."

Grichuk's homer, his 18th of the season, came off Bumgarner's replacement, right-hander Matt Cain (3-11), with two outs in the second. The homer also scored Jose Martinez, who singled one out earlier.

The Cardinals led just 2-1 before adding one run in the seventh and two in the eighth against the San Francisco bullpen.

Pham's third hit of the game, a single, drove in pinch hitter Greg Garcia in the seventh, increasing St. Louis' lead to 3-1.

Right-hander Mark Melancon, the Giants' fourth pitcher, walked in a run and hit Pham with the bases loaded in the eighth as the Cardinals pulled away into a four-run lead.

Wacha allowed just four hits. He walked two and struck out two.

"I felt good out there," he said. "The defense played great behind me."

Right-hander Matt Bowman and lefty Tyler Lyons followed Wacha with one scoreless inning apiece before the Giants opened the ninth with back-to-back doubles against righty John Brebbia.

The second of the doubles required a four-minute review from New York that erased what had been ruled on the field as a home run for Crawford.

The shortstop's shot toward the right field foul pole was caught by a fan near the top of a green awning that separates the 25-foot-high wall from the pole.

Upon review, it was determined that the ball would have hit the awning if not interfered upon by the fan, and Crawford was given a ground-rule double.

"I was told that they saw a fan reach over the fence," Crawford said. "I'd like to see that camera angle, because everyone at the park saw something different.

"For somebody to reach into the field of play, they'd have to lay flat (on the awning) and somebody would have to hold their feet."

After Brebbia got Hunter Pence to fly to right field for the first out, left-hander Zach Duke and closer Seung Hwan Oh recorded one out apiece to protect the 5-2 lead.

Oh was credited with his 20th save.

Pham's three hits included a double, one of three extra-base hits the Cardinals had among their 10 hits.

Grichuk had two hits and scored twice for the Cardinals, who improved to 2-1 on their 10-game trip.

Crawford had two doubles. Buster Posey, returning to the lineup after missing the three-game series against the San Diego Padres with a bruised thumb, chipped in with a double and a single for the Giants, who were opening a four-game homestand.

The Giants have totaled just 12 runs in their past seven games.

Cain left for a pinch hitter in the fifth inning, having allowed the two runs produced by Grichuk's homer and seven hits. He struck out two and did not issue a walk.

He took his 10th consecutive loss, tying a franchise record set by right-hander Bill Lohrman in 1940.

Pinch-hitting for Cain, Carlos Moncrief got the Giants within 2-1 in the fifth with a sacrifice fly to deep center field, scoring Pence.

NOTES: Giants manager Bruce Bochy announced before the game that the earliest LHP Madison Bumgarner (illness) might make his next start is Sunday. ... RHP Matt Cain's 10-game losing streak is the longest in the majors since RHP Shelby Miller lost 16 straight in 2015. ... The Giants plan to activate RHP Johnny Cueto (blisters, strained flexor tendon) off the 10-day disabled list on Friday and start him in the second game of the series. He hasn't started for San Francisco since July 14 at San Diego. ... The Cardinals are expected to promote RHP Jack Flaherty from Triple-A Memphis in time to start the Friday game. ... The Cardinals recalled RHP John Gant from Triple-A and designated LHP Kevin Siegrist for assignment. Siegrist (strained left forearm) was reinstated from the DL to make the transaction possible.