Manager Tony La Russa thought Pineiro, who had become dehydrated, should have left triumphant. Instead, the right-hander suffered his eighth defeat in his last nine decisions.
"In the first inning, he deserved a little better than that," La Russa said. "He pitched a strong game."
Pineiro retired 16 batters in a row from the first through the sixth. He threw first-pitch strikes to 20 of the 27 hitters he faced and, for the sixth time this season, didn't walk a batter.
"I thought he did a really good job of continuing to compete after a really tough first inning," La Russa said. "That's a shame for him to be the losing pitcher."
The key misplay was an error by third baseman Joe Thurston, making three of the four runs Pineiro allowed unearned.
Pineiro should be ready to make his next start Tuesday in New York against the Mets.
Tigers 6, Cardinals 3: After spotting Detroit rookie RHP Rick Porcello a four-run lead in the first, the Cardinals had him on the ropes in the second. They pushed two runs across and had runners at first and third with nobody out.