ST. LOUIS -- Milwaukee Brewers left fielder Khris Davis ran his team out of the fourth inning Friday night with a mental error most Little Leaguers wouldn't have committed.

Davis made up for it in the ninth.

His leadoff homer off St. Louis Cardinals closer Trevor Rosenthal snapped a tie and led Milwaukee to a 4-3 win at sold-out Busch Stadium that added insult to injury for the home team.

After losing starter Carlos Martinez seven pitches into the game with right shoulder tightness, the Cardinals (97-57) then hacked up a 3-1 lead and saw their National League Central lead over second place Pittsburgh shrink to three games.

Davis, who was 1-for-5 with four strikeouts against Rosenthal (2-3) prior to the ninth, lined a 1-1 fastball into the St. Louis bullpen in right-center for his 24th homer of the year.

"Spoiler alert," Davis said.

Spoiling is about all the Brewers have had to play for since a 5-18 start that cost manager Ron Roenicke his job four weeks into the season. Ravaged by injuries that have deluded them of middle-of-the-lineup threats such as right fielder Ryan Braun and catcher Jonathan Lucroy for long stretches, Milwaukee appreciates any win against a contender.

"We're still in there fighting," said reliever Will Smith (7-2), who wriggled out of a two-on, no-out jam in the eighth to earn the win. "It's nice to come in here and play a close game, and pull it out."

Smith got help from catcher Martin Maldonado, who nailed pinch-runner Peter Bourjos trying to steal third after shortstop Jhonny Peralta fanned on a 3-2 pitch for a double play. Smith then induced a popup from hot-hitting rookie left fielder Stephen Piscotty, who has five RBI in the series' first two games.

Davis then expunged his mistake of the fourth, when he ran into an inning-ending double play in the fourth as he forgot the number of outs and was caught off second on a routine fly ball.

"You can write that," he said when asked if the homer erased his mental error. "It felt good."

By contrast, very little about this one felt good for St. Louis, starting with the early departure of Martinez. Feeling tightness in his right shoulder, Martinez tried to pitch through it but had to leave the mound after throwing a strike to first baseman Adam Lind.

An emotional Martinez held his glove over his face as he walked off the mound, but later said he felt he could return to the starting rotation before the Cardinals' regular season ends next weekend in Atlanta.

"Something seemed off," catcher Tony Cruz said. "He didn't throw many pitches in warmups, and I saw his fastball was 89 (mph) on the double (to second baseman Scooter Gennett). He wanted to stay in, but this was the right move."

It became a bullpen game for St. Louis, which used a whopping eight pitchers. It got 3 2/3 effective innings from long reliever Tyler Lyons and carried a 3-1 lead to the sixth as Cruz had a hand in both rallies, doubling and scoring in the third and then lofting a sacrifice fly an inning later.

But the Brewers (65-89) pecked away, drawing within 3-2 in the sixth on a two-out pinch-hit RBI single by Lucroy, then tying it an inning later when shortstop Jean Segura sped home from second on a two-out error by second baseman Greg Garcia.

Milwaukee's bullpen fired four scoreless innings after starter Ariel Pena worked through five innings, allowing six hits and three runs with a walk and five strikeouts.

Closer Francisco Rodriguez earned his 36th save, pitching around a leadoff single by Garcia. Rodriguez fanned pinch-hitter Randal Grichuk -- the 43rd player used in the game -- and third baseman Matt Carpenter with Garcia at second to end it.

NOTES: St. Louis gave 2B Kolten Wong the night off, with INF Greg Garcia starting in his place. Wong is locked in a 2-for-20 skid that's lowered his average to .262. ... Milwaukee RF Ryan Braun (lower back tightness) missed his seventh straight start. There is no timetable for his return. ... OF Jason Heyward is the second right fielder in Cardinals history with at least 32 doubles and 23 steals in the same year. The other is Pepper Martin, who had 36 and 23 back in 1936.