In his final five starts, Marquis (14-16) had one stint of one inning and another of two. He allowed 18 runs in 22 1/3 innings.
"We played like we pitched," manager Tony La Russa said, "which was not good. The first four innings (eight runs), we pitched poorly and we played poorly. Then we pitched better and we started playing better."
Marquis' fall has puzzled La Russa and his staff.
"It's a head-scratcher, man," La Russa said. "His location is poor. I don't care how good your stuff is, you've got to locate in this league."
Asked about a potential next start for Marquis, La Russa said, "This is not a good time to ask. That was a disappointing performance. He's disappointed, too, so I don't want to pile on him.
"He's not going out there and nonchalanting it. (But) we needed him to be better, and he wasn't."
REPLAY: Right-hander Jason Marquis probably lost out on a postseason starting assignment -- if there is a postseason for the Cardinals -- when he was assaulted for six runs while getting only six outs Thursday in a 9-4 loss to Milwaukee.
The Cardinals scored three runs in the eighth inning, one on Scott Rolen's 22nd homer and two more on a double by Preston Wilson, who earlier had homered, but that was far too late to prevent the club's eighth loss in the last nine games and ninth in the last 11.
--The half-game lead for the Cardinals is their smallest since they were tied for first with Cincinnati on Aug. 24.
--SS David Eckstein still is having trouble with his left hamstring and isn't expected to play Friday night in a cold-weather game at Busch Stadium.
--1B Albert Pujols had a seven-game hitting streak snapped when he went 0-for-4 Thursday.
--RHP Jason Marquis' 16 losses are the most for a Cardinals pitcher since 1990, when Jose DeLeon lost 19 and Joe Magrane lost 17.
Marquis has given up 78 runs at Busch Stadium this season, 11 more than any other pitcher at home.