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The St. Louis Cardinals' lead atop the NL Central has gotten more uncomfortable during a rocky start to their long West Coast trip.

They're hoping Michael Wacha can help them snap out of their funk.

The San Diego Padres look to sweep this three-game series with a season-high sixth straight win Sunday at Petco Park.

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St. Louis (77-45) has dropped four of six after losing the first two of a 10-game road trip and was shut out for the second time in its last four with Sunday's 8-0 defeat.

Pittsburgh, meanwhile, has won eight of 10 after beating San Francisco earlier in the day to pull within 3 1/2 games of the Cardinals. St. Louis came apart in the seventh inning Saturday, as the Padres (61-62) sent 12 hitters to the plate and scored seven times.

''It was not a good night offensively,'' said Matt Carpenter, who was ejected in the fifth for arguing balls and strikes. ''(Padres starter Ian) Kennedy threw the ball well. He kept throwing the ball off the plate and he was getting some calls.''

Wacha (14-4, 2.85 ERA) looks to help St. Louis get back on track. He's 3-0 with a 1.00 ERA over his last four starts after pitching seven solid innings in the Cardinals' 2-1 win over San Francisco on Monday.

It marked the third time in that stretch he's gone seven innings after going at least that many just once in his previous eight.

The right-hander hasn't had a full season in the majors after being a late call-up in 2013 and spending nearly three months on the disabled list last year. His 145 1-3 innings are 38 1-3 more than he tossed in 2014.

"I hated not throwing him back out there (for the eighth inning Monday)," manager Mike Matheny said. "Part of it is that we're going to have to watch him."

Wacha also was lifted after seven when he faced the Padres on July 3 after giving up a homer to Jedd Gyorko leading off that inning. He didn't factor into the decision of the Cardinals' 2-1 loss.

The Padres are the only NL team with a winning record against the Cardinals having taken four of six meetings. They are on the verge of getting back to .500 for the first time since they were 32-32 on June 13 after Matt Kemp had a two-run single and Justin Upton added a two-run double in the big seventh inning Saturday.

Kemp is hitting .375 with four homers and 15 RBIs during a 14-game hitting streak.

San Diego has won nine of 11 and looks to keep rolling behind Colin Rea (2-0, 4.22), who can join Dave Freisleben (1974) as the only Padres to win their first three career starts.

Rea beat Cincinnati 11-6 in his major league debut Aug. 11 before giving up two runs in 5 2-3 innings of Monday's 5-3 win over Atlanta. The right-hander admitted to being more focused in his second outing.

''I thought he was better (Monday),'' interim manager Pat Murphy said. ''Breaking ball was good; little baby cutter, good; even threw a splitter or two that was good. I thought he commanded his fastball for the most part. I was real pleased with what he did. He showed great poise again. You've got to take notice.''

It's unclear who will be catching for Rea after Derek Norris suffered a bruised left hand in the eighth inning Saturday. He went to his knees for several minutes after a pitch deflected off him before being taken out of the game.