The slumping Mulder gave up two home runs to left-hander Adam Dunn and a two-run double to Ken Griffey Jr., another left-hander, as Cincinnati scored seven runs in the first three innings and held on for a 7-6 win on Wednesday.
"My location's been terrible," said Mulder (8-5), who is 1-4 in his last five starts. "On and off, it's been like that all year. It's getting to be frustrating. I'm not finishing pitches."
Left-hander Sean Casey also had two hits against Mulder, who went into the game allowing left-handers to bat just .125 against him. Dunn's home runs were the first Mulder allowed to left-handers all season.
"He was having location problems, and they capitalized," manager Tony La Russa said.
Mulder, who was acquired from Oakland in an offseason trade, allowed season highs of 12 hits and seven runs in four innings. His previous season highs were 11 hits, by the Reds in his 6-5 loss on April 13, and six runs by Cincinnati and two other teams.
Dunn led off the second and third innings with home runs, his 19th and 20th of the year. The Reds jumped out to a 7-0 lead while improving to 2-0 under interim manager Jerry Narron, who was promoted from bench coach on Tuesday to replace the fired Dave Miley.
"I told (Dunn) if he hits three, he's leading off Friday," Narron said.
Dunn struck out leading off the fifth inning.
Reds starter Ramon Ortiz (3-5) didn't allow a hit in his first career appearance against St. Louis until Mark Grudzielanek led off the fifth with his seventh home run of the season. Ortiz gave up five hits and three runs in seven innings for his second win in his last three starts.
"I feel good," Ortiz said. "I had a good breaking pitch, a good changeup, a good slider, and a good fastball, inside and outside. When your team scores seven runs, that's very good. When they score runs for you, you have to go get it. You have to throw strikes and make your pitch."
The Cardinals scored three runs in the eighth inning to cut the lead to 7-6 before David Weathers pitched out of trouble. He went 1 2/3 innings before Kent Mercker struck out Jim Edmonds with a slider for the final out in the ninth and his first save in three tries.
"Our bullpen stopped the bleeding, and we kept plugging," La Russa said. "We had a good-looking rally, but they made pitches when they had to. Weathers got the outs they needed and Mercker made his pitches."
The save was Mercker's first since Aug. 27, 2003, for Atlanta against the New York Mets.
"The infamous backdoor slider," Mercker said. "If you can learn how to throw that pitch, you can make a lot of money. He's a guy you want to stay away from, but you'd better make sure it's down."
"I like Mercker and Weathers at the end," Narron said. "They give you everything they've got, they battle, and they don't beat themselves."
Joe Randa gave the Reds a 1-0 lead by driving in Rich Aurilia from second base with a two-out single in the first. Mulder gave up three hits in the inning, which matched the total he gave up over seven shutout innings in the Cardinals' 7-3 win over the Reds on May 4.
Dunn sparked Cincinnati's four-run second by leading off with his 19th homer. Aurilia added an RBI single and Griffey hit a two-run double to the base of the center-field fence.
Dunn led off the third inning with his second homer, giving him four multihomer games this season and 13 in his career. Jason LaRue followed with a single, moved to third on Ortiz's double and scored on Aurilia's one-out single to center.
The Cardinals added two runs after Grudzielanek's homer in the fifth.
- Dunn's homers gave him six this season off left-handers, including his last three. The left-handed hitter went into the game hitting .162 against left-handers.
- Randa extended his hitting streak to eight games (10-for-29, .345).
- Ortiz's double was his second career hit and first for extra bases in 42 at-bats.
- Edmonds started for the first time on the nine-game road trip and extended his hitting streak to five games (7-for-19, .368). He missed the previous eight games with a hairline fracture of his left middle rib.
- The Cardinals had won six consecutive series before dropping two of three on this road trip.