"It's something you go to sleep thinking about and you wake up thinking about it and wonder what that sick feeling in your stomach is when you get up," Matheny said.
"You realize it's because we haven't been doing what we're supposed to do, what we're paid to do, and that's win ballgames."
The Cardinals ended their season-worst seven-game skid Thursday night and did so in emphatic fashion, averting a five-game sweep by routing the Pirates 13-0 in a matchup between the NL's top two teams.
St. Louis began the series with a 2½-game lead in the NL Central, but left with the Pirates ahead by 1½ games. The Cardinals avoided their first sweep in a set of at least five games since 1916, when the New York Giants took all six games.
Pittsburgh had won the previous four games at PNC Park by a combined score of 36-10.
"We had kept the cat in the bag for four games," Pittsburgh manager Clint Hurdle said. "Tonight, we let it out."
Joe Kelly (2-3) pitched six scoreless innings and had two hits. Tony Cruz added three hits, including a two-run double during an eight-run seventh inning.
Kelly allowed three hits while walking four and striking out four. Seth Maness, Michael Blazek and Edward Mujica pitched one inning each to complete the five-hitter.
"It felt good," Kelly said. "The whole time going out there I was just trying to pitch as best as I could. I just wanted to compete my butt off and try as hard as I could to help us get that win."
After the Cardinals failed to acquire a replacement for injured All-Star catcher Yadier Molina prior to Wednesday's non-waiver trading deadline, Cruz figures to get the majority of starts behind the plate. He had started just 11 games this season until Molina went on the disabled list Wednesday with a sprained right knee.
Carlos Beltran, Allen Craig, Matt Holliday and David Freese also had two of St. Louis' 17 hits. Craig came into the game in a 1-for-27 slump, and he had a two-run double in the seventh.
Charlie Morton (3-3) struggled against the Cardinals again, giving up five runs and 10 hits in six innings. He is 2-8 in his career against St. Louis.
"I made some bad pitches, some pitches that I could executed better and other that I wasn't smart about," Morton said. "I'm not saying they wouldn't have scored any runs, but I could gone about it better."
Morton threw a wild pitch that made it 1-0 in the second. St. Louis scored three times in the fourth as Jon Jay was hit by a pitch with the bases loaded, Cruz grounded into a double play and Pete Kozma had an RBI single.
Beltran doubled in a run in the sixth before the Cardinals broke the game open an inning later.
"Today was a good sign for our team," Craig said. "There was no panic. We brought a lot of energy. You hate to go into lulls like we did because we've played so well all season long but I think this game should get us going again."
NOTES: CF Starling Marte had two of Pittsburgh's five hits. He has a hit in all 12 career games against the Cardinals. ... Pittsburgh C Russell Martin sat out the game with a sore left knee. ... St. Louis opens a three-game series Friday night at Cincinnati with RHP Shelby Miller (10-7, 2.79) facing RHP Bronson Arroyo (9-8, 3.26). ... RHP Gerrit Cole (5-4, 3.56) will pitch for Pittsburgh on Friday night in the first game of a three-game series against Colorado's Jhoulys Chacin (9-5, 3.54).