In a doubleheader that featured a battle of aces on Saturday, the St. Louis Cardinals dominated the San Francisco Giants by a combined score of 15-1. The Giants’ starting rotation was exposed badly once again.

The Cardinals defeated the Giants 8-0 and 7-1 behind stellar pitching performances from Shelby Miller and Adam Wainwright. Miller and Wainwright combined to strike out 17 while allowing just one run on 14 hits and one walk over 16 innings.

The 22-year-old Miller is now 6-3 with a 1.82 ERA on the year. He’s struck out 72 against 17 walks over 69.1 innings. Wainwright is 8-3 with a 2.33 ERA. His 84-to-6 strikeout-to-walk ratio over 89 innings this season is exceptional.

The Cardinals entered play on Saturday with the game’s best rotation ERA at 2.58. Not surprisingly, they also have the best record in baseball.

The defending World Series champion Giants are just 29-27 after getting swept by the Cardinals. The Giants’ lack of consistency this season is due to the struggles of the starting rotation.

The Giants won two out of the last three World Series titles in large part because of the outstanding work of the rotation. The Giants’ rotation finished sixth in ERA last year, second in 2011 and third in 2010. Thus far in 2013, the starters have not been up to the task.

The Giants came into the doubleheader ranked 24th in baseball with a 4.77 ERA from the starting rotation. They were 26th in quality starts with just 22 through the first 54 games.

The two aces of the staff—Matt Cain and Madison Bumgarner—both failed to deliver a quality start on Saturday. While Miller and Wainwright were mowing the Giants down, Cain and Bumgarner were getting blasted by the Cardinals.

Cain and Bumgarner combined to allow 15 hits and 12 runs over 12 innings of work. The third inning was particularly confounding for both pitchers.

Cain allowed nine hits and seven runs in the third. He didn’t allow any baserunners in his other five innings of work.

Cain now has a 5.45 ERA after his rough outing against the Cardinals. His career ERA entering this season was 3.27.

The culprit for his rough start to 2013 has been his lack of command within the strike zone. In the third inning against the Cardinals, that problem was obvious as he continued to make location mistakes right over the middle of the plate.

After Cain’s start, Alex Pavlovic of the San Jose Mercury News wrote:

Last season, Cain never allowed six runs in a game. He has done it four times through 12 starts this season…

‘I can’t think of a time like this,’ Cain said, when asked if he could remember grooving as many fastballs down the plate, which is really what this comes down to. ‘It’s about trying to get the rhythm back.’

Cain said he would go back again and look at what happened and then move on. Maybe he’ll find something he missed during the first glance, but at the moment, he doesn’t have many answers. Why is he missing location so often?

‘I couldn’t tell you right now,’ he said.

After retiring the first seven batters during the second game of the doubleheader, Bumgarner walked Pete Kozma with one out in the third. He then left an 0-2 pitch out over the plate to Wainwright, who smashed it for a double.

After a grounder off the bat of Jon Jay scored a run, Bumgarner left another two-strike pitch out over the plate to Carlos Beltran. Beltran lined a two-run single to center to make the score 3-0.

Bumgarner had taken over for the struggling Cain as the staff ace in April when he went 3-0 with a 1.55 ERA. However, during May, he went 1-3 with a 5.17 ERA before getting hit hard in his first start of June. His 3.46 ERA still leads the staff.

Barry Zito is second in the rotation with a 3.88 ERA. It’s been a tale of two seasons for Zito. He’s 4-0 with a 1.40 ERA in seven starts at home compared to 0-3 with a 10.19 ERA over four starts on the road.

No other starter on the staff has an ERA below the league average of 4.17. Cain (5.45 ERA), Tim Lincecum (5.12) and the injured Ryan Vogelsong (7.19) have all struggled this year.

Vogelsong‘s replacement, Michael Kickham, was knocked out in the third inning of his only start after allowing four runs. He was demoted back to Fresno and replaced in the rotation by long reliever Chad Gaudin.

Two months into the season, the Giants can no longer chalk up the disappointing performance of the rotation to a small sample size fluke. They also can’t move each struggling starter to the bullpen because they have no clear alternatives. Kickham was the organization’s top starter in the upper minors, and he didn’t look ready for the show during his debut.

The good news for the Giants is that they’re only two games out of first place despite the rotation’s ugly performance. Given the impressive track records of Cain, Bumgarner, Lincecum and Vogelsong, the Giants have to figure that they’ll receive improvement from their starters at some point this year.

However, with Vogelsong out for up to eight weeks, general manager Brian Sabean may need to turn to the trade market to stabilize the rotation. Sabean should already be scouring the market for potential trade options even though the trading deadline is nearly two months away.

If Sabean‘s troops keep getting exposed as badly as they did on Saturday, he will need to strike early to bring in reinforcements. Otherwise, the Giants risk digging a hole that will be too deep to climb out of.

Losing by a combined score of 15-1 in Saturday’s doubleheader should serve as a wake-up call. The Cardinals’ two aces were exceptional. The Giants’ two aces pitched like fifth starters. That’s not a recipe for defending a championship.

 

All statistics in this article are courtesy of ESPN and Baseball-Reference.

Read more MLB news on BleacherReport.com