ST. LOUIS -- His hold on a rotation spot already tenuous, Justin Masterson did nothing to boost that job security on Saturday. Masterson could not last through the fifth, knocked out by an overpowering Cubs lineup that led Chicago to a 5-1 victory in Game 1 of a day-night doubleheader at Busch Stadium.
One night after bashing four homers, the Cubs connected for three more, giving them as many in 18 innings as the Cardinals had hit over their last 18 games. St. Louis' labor-intensive offense couldn't answer against Chicago lefty Felix Doubront, leaving the Cardinals with a sixth loss in eight games.
"This is a team that is really capitalizing on the home run," manager Mike Matheny said of his opponent. "They are productive with the hits. You look at it, we both had seven hits, but theirs did some damage and had better timing."
All of that damage was done against Masterson, who has yet to give the Cardinals much positive return from the Trade Deadline deal in which they swapped outfield prospect James Ramsey for the veteran sinkerballer.
Hopeful of guiding Masterson back to 2013 form, the Cardinals have spent the last month helping him simplify his mechanics. Improved results haven't followed.
He allowed five runs -- three via solo homers -- before being chased with one out in the fifth. The Cubs' other two runs came in the second, an inning extended when Masterson walked Doubront on five pitches. Chris Coghlan followed with a two-run single, the second run added to the scoreboard after a replay overturned an out call at the plate.
"The inconsistency," Masterson noted afterward. "I had some great at-bats and then wouldn't finish some pitches, leaving them up and in. They're hitting the ball hard when you leave them right there."
It marked the fourth time in Masterson's six starts with the Cardinals that he had been tagged for five runs. With Cleveland, opponents reached that five-run mark in nine of Masterson's 19 starts. He's been unable to pitch beyond the fifth in all but two starts since the trade.
Also of concern was the lack of ground-ball outs. Masterson had only four in all, all consecutively after Coghlan's hit when the right-hander provided a brief glimmer of the potential the Cardinals had hoped would emerge.
"Whenever they get the ball in the air off him, something isn't exactly right," Matheny said. "He's a ground-ball guy. He's a machine when he's locked in. Not just the home runs, but you're seeing fly balls. You're seeing popups. All of those things are very atypical of a guy with a power sinker. He has to keep working. He has to find it."
Where does Masterson turn next?
"Just execute. That's it. It's not rocket science," he said, trying to mask the frustration with a smile. "It's just not working. I'm not executing. I think right now I'm just fired up, so it's probably best not to even try and talk about it right now."
Masterson's spot in the rotation will next come up on Thursday, when the Cardinals open a key series in Milwaukee. The likelihood of Masterson making that start appears slim, and the club may have found a capable replacement (at least a temporary one as the Cards await Michael Wacha's return) upon Masterson's departure on Saturday.
Tyler Lyons relieved Masterson and sailed through the game's final 4 2/3 innings to preserve the rest of the 'pen. He faced the minimum and struck out eight, the most by a Cardinals reliever since Mark Littell also fanned eight in a 1978 appearance against the Dodgers.
Asked if a change would be coming, Matheny responded that it was "too early to make that statement." Minutes later, Lyons earned an endorsement from, of all people, Masterson.
"That was pretty impressive the way he went out there," Masterson said. "If we had known that, we should have started him."
A scuffling St. Louis offense had little support to offer Masterson, scoring only on a Jon Jay double-play ball in the second. Jhonny Peralta's leadoff double and a single by A.J. Pierzynski set up the scoring opportunity. Doubront scattered seven hits (six singles) over seven innings, his longest start of the year.
Following a string of 10 straight games with four or more runs scored, the Cardinals have plated 10 runs over their last six games. Every opposing starter to face them during that stretch has exited with a quality start.
"We were hoping he'd be very efficient with his pitches and he was," Cubs manager Rick Renteria said of Doubront. "That's a pretty good lineup, and he did a nice job of containing them."
Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, and follow her on Twitter @LangoschMLB. This story was not subject to the approval of Major League Baseball or its clubs.