The Cardinals took two out of three against the Mariners to keep pace with the Pittsburgh Pirates, who also won Sunday.
Matt Adams hit a two-run homer for St. Louis and Shelby Miller (14-9) threw five innings for the win, giving up two runs -- one earned -- on three hits and two walks.
The Cardinals had 19 hits and secured their sixth home series win in a row, including two against the Pirates. They went 7-2 on a nine-game homestand.
Cardinals manager Mike Matheny said the team has been talking about having a breakout offensive effort.
They got it Sunday.
"It was great timing. It will send us on the road with some good feelings about their swings," said Matheny.
Erasmo Ramirez (5-2) allowed five runs and eight hits in five innings for the Mariners, who have dropped six of seven. He was the first Seattle starter in the series to give up any runs.
The Cardinals took a 5-1 lead with a four-run fourth -- four runs coming on singles by Daniel Descalso, Matt Carpenter and Matt Holliday. Carpenter's hit scored two.
Abraham Almonte knocked in a run for Seattle on a sac fly in the fifth, but St. Louis tacked on four more runs in the bottom of the inning on Adams' homer and RBI singles by Descalso and Jon Jay to make it 9-2.
In the seventh, Holliday delivered an RBI double and Carlos Beltran hit a two- run single for an 11-2 lead.
Earlier, Molina led off the second with his 12th home run of the season. It was the first hit by either team.
"They really put it together today," Mariners manager Eric Wedge said of the Cardinals. "They have a good veteran lineup."
The Mariners didn't have a hit off Miller until Almonte's leadoff double in the fourth. Almonte later scored on Franklin Gutierrez's single to tie the game.
Mariners starters Hisashi Iwakuma (seven innings) and James Paxton (six) held the Cardinals scoreless in the first two games ... The Mariners continue a 10- game road trip with a four-game series in Detroit starting Monday ... The Cardinals start a seven-game road trip Monday at Colorado.
09/15 22:53:10 ET