ST. LOUIS -- As the schedule dwindles to its final two weeks, the Cardinals have little margin for error. They certainly have no room for two errors in the same inning.

Just such an unraveling doomed them on Wednesday night, with a pair of Felipe Lopez miscues turning a one-run inning into a four-run outburst. The ugly frame sent St. Louis to a 4-3 loss to the Cubs, ending a three-game winning streak and knocking the Cards back to 4 1/2 games behind Wild Card-leading Milwaukee.

With two on and one out in the second inning of a tie game, Lopez played for a tag rather than a force out on a bunt play at third base, allowing the Cubs to load the bases. One batter later, his throw to second on a potential double-play ball skipped to the outfield. When the next Chicago batter grounded out, the inning should have been over with a 1-1 score intact.

Instead, the Cubs hung three unearned runs on Braden Looper, and it was too tall a hill for the Cardinals to climb. St. Louis now stands in fourth place in the Wild Card race, falling behind Houston as well as Milwaukee and Philadelphia. The Cards are also in fourth in the National League Central.

"It was an ugly inning," said manager Tony La Russa, "but that's part of baseball."

Looper has been a hard-luck starter lately. In his past 10 starts, he's held the opponent to two earned runs or fewer eight times, yet he has a 3-5 record in that span.

Albert Pujols' RBI groundout in the first inning gave Looper and the Cards an early lead, but the edge vanished quickly. Three consecutive singles opened the second inning and tied the game, and after that, Lopez's errors turned the inning into a slog. Looper needed 46 pitches to escape the frame.

Ted Lilly attempted a sacrifice bunt with runners on first and second, and Yadier Molina's throw appeared to beat Mark DeRosa to third base. But because Lopez didn't have a foot on the bag, DeRosa was ruled safe and the bases were loaded with no outs.

"I kind of got messed up there," Lopez said. "It's my fault. It's a force out, but I tried to tag him. It was a good throw [from Molina]. ... There's no excuses. I messed up. I went to tag the guy."

The next batter, Alfonso Soriano, hit a potential double-play ball to Lopez, but Lopez's throw to second base scooted into the outfield, and two more runs scored. Ryan Theriot's ground ball should have been the third out, but instead it was the first, and Derrek Lee's fielder's choice grounder scored Lilly for the fourth run.

"I was just trying to hurry," Lopez said. "[Soriano] is a fast runner. I was just trying to be aggressive and trying to get a tough play, and I didn't get a good grip on the ball. I just tried to hurry up and throw it."

Looper lasted three more innings without allowing another run, but the Cards couldn't mount enough of a comeback, though Ryan Ludwick made it interesting, drilling his 33rd homer in the ninth, a two-run shot that brought the Cards within a run, at 4-3. Looper likely would have made it well beyond the fifth if not for the fateful second.

"Basically, we didn't win," he said. "I let the first two guys on base in the second. If I don't do that, we probably win the game. I let the first two guys get on. After that, it seemed like every time they touched the bat, they found a hole or got a break."