The St. Louis Cardinals still can't find all the answers as they try to add to their lead in the postseason race.

Logan Forsythe and Alexi Amarista had key hits in a five-run fourth inning, and the San Diego Padres beat the Cardinals 6-4 Tuesday night to send the slumping World Series champions to their 10th loss in 14 games.

St. Louis maintained a one-game lead over the Los Angeles Dodgers for the NL's second wild-card berth but dropped 10½ games behind Cincinnati in the NL Central.

The only saving grace for the Cardinals is that the teams directly behind them have played as bad or worse then them.

"The bottom line is we have to win, regardless of if the other teams in contention are losing or not," third baseman David Freese said.

"This is a good opportunity to lengthen our lead in the standings and we are not doing it. It's putting more pressure on this team and allowing other teams to stick around," he said.

While the Dodgers and Pittsburgh both lost, Milwaukee and Philadelphia have both crept to within four games of the Cardinals.

"It doesn't seem like there are any breaks when things are going bad," St. Louis second baseman Skip Schumaker said. "It's where we are at right now, and it's tough. We are letting other teams in and it's going to make these next couple of weeks interesting."

Freese provided one of the few spots for the Cardinals with a solo homer in the seventh that cut San Diego's lead to 5-4. But St. Louis was just 1 for 14 with runners in scoring position and stranded 13 runners. The Cardinals have lost seven of their last eight road games.

"We had a lot of chances in the middle of the order, where we want it to be," St. Louis manager Mike Matheny said. "We just didn't get it done."

Since Aug. 22, the Cardinals have held onto the last NL wild-card spot despite an 8-11 record. But the Dodgers are 7-10 and the Pirates have gone 5-12.

Forsythe, a homer shy of the cycle in Monday night's 11-3 win over St. Louis, doubled in two runs and Amarista added a two-run triple as San Diego erased a 2-0 deficit in the fourth.

Edinson Volquez (10-10) allowed three runs — two earned — and four hits in 5 1-3 innings, striking out six and walking six. He has a career-high 100 walks, the most in the majors this season.

Luke Gregerson pitched 1 2-3 innings for his sixth save in 10 chances, finishing San Diego's 16th win in 21 games.

"We're playing good ball right now," Forsythe said. "Big hits in big situations. We're having fun."

Since Aug. 14, the Padres have a 10-4 record against teams with winning records.

Adam Wainwright (13-13), hurt by rookie shortstop Pete Kozma's error in the fourth, gave up five runs — two earned — five hits and four walks in six innings. He had been 3-1 with a 1.07 ERA in seven career appearances against San Diego.

"He looked better," Matheny said. "He was spotting his fastball a little better and his curveball was pretty sharp. He used it a lot and they weren't on it until the fourth."

With St. Louis ahead 2-0 in the fourth, San Diego loaded the bases with one out when Kozma threw wildly on Will Venable's grounder, and Chase Headley and Yasmani Grandal reached on infield singles. Yonder Alonso walked on a full-count pitch, forcing in a run, and Forsythe hit a two-run double to right-center for a 3-2 lead.

After Alonso got thrown out at home trying to score on Cameron Maybin's grounder to Schumaker, Amarista hit a two-run triple into the right-field corner.

Jon Jay's RBI single in the sixth off Joe Thatcher and Freese's homer against Brad Brach pulled the Cardinals to 5-4. Cameron Maybin had an RBI single off Edward Mujica in the eighth.

St. Louis loaded the bases with no outs in the second but scored only one run, on Schumaker's groundout. Volquez got out the jam by getting Kozma to ground into a double play. Shortstop Everth Cabrera's error on Yadier Molina's grounder allowed Jay to score in the third.

Alonso, who walked three times, hit his 34th double of the season in the eighth, breaking the San Diego rookie record set by Benito Santiago in 1987.

NOTES: Wainwright's only other loss to the Padres came at San Diego on May 25, 2010, when he tied a career high with 12 strikeouts over seven innings in a 1-0 loss. ... Wainwright had walked just 43 batters in his previous 28 starts over 173 2-3 innings. ... Padres LF Carlos Quentin, who was removed from Monday night's game, was out of the starting lineup Tuesday with a sore right knee. ... Cardinals RHP Kyle Lohse (14-2, 2.81 ERA) opposes Padres LHP Clayton Richard (12-12, 3.78) in the series finale Wednesday.