Gene J. Puskar, Associated Press
St. Louis Cardinals pitcher Joe Kelly, left, is congratulated by teammate Adam Wainwright (50) in the dugout after finishing the seventh inning of a baseball game against the Pittsburgh Pirates in Pittsburgh, Sunday, Sept. 1, 2013. The Cardinals won 7-2.

PITTSBURGH — There are more comfortable ways to make your first major league start than in the middle of a playoff race.

Still, Kris Johnson wouldn't have it any other way, even after the Pittsburgh Pirates rookie left-hander stumbled through a 7-2 loss to St. Louis on Sunday that left the Pirates and Cardinals tied atop the NL Central with four weeks left in the season.

"These are the kind of situations you want to be put in," Johnson said. "I just didn't take advantage of them when I had the chance. I worked all my life to get here and to fall short today, (I'm) just going to have to get back on the field, get back on the throwing program and get back to where we were before."

Johnson (0-2) sparkled after being pressed into action in his big league debut two weeks ago against Arizona, pitching six innings in relief only hours after being called up from Triple-A Indianapolis.

Given more notice about his spot start while the Pirates rested struggling Jeff Locke, Johnson was far less effective. Shaky from the outset, he gave up five runs and seven hits in two-plus innings.

"Give (St. Louis) credit, but he didn't come anywhere near having the command he did today that he had against the Diamondbacks," Pittsburgh manager Clint Hurdle said. "To me, that was the difference."

Justin Morneau went 1 for 3 in his Pirates debut a day after being acquired from the Minnesota Twins. Marlon Byrd, picked up last week from the New York Mets, went 2 for 3 but the Pirates will head to Milwaukee for the start of a pivotal nine-game road trip even with the Cardinals.

Matt Holliday and David Freese drove in two runs apiece for St. Louis. Matt Carpenter, Allen Craig, Yadier Molina and Shane Robinson added two hits each for the Cardinals, who snapped a three-game slide by pounding Johnson early.

The National League's best offense scored all of one run combined during its brief skid but bounced back by waiting out Johnson and then pouncing when he made a mistake.

Carpenter doubled to open the game and Robinson followed with a walk. Craig and Molina provided consecutive RBI singles, and Jon Jay added a sacrifice fly to stake Kelly to a 3-0 lead before he threw his first pitch.

The advantage grew in the third when Freese doubled to score Craig and Molina and end Johnson's day.

"We didn't do ourselves any favors by falling behind in the count. Then he tried to force a couple pitches and got us in trouble," Pirates catcher John Buck said. "With a team like that you can't make mistakes like that."

Joe Kelly (7-3) allowed one run and four hits in six solid innings to win his fourth straight start. The right-hander struck out five and walked two to remain unbeaten since June 5.

Kelly's emergence has helped stabilize an injury-riddled St. Louis rotation as the Cardinals prepare for an NL Central race that could go down to the wire.

The Pirates reclaimed first place with a 7-1 victory Saturday night, but St. Louis responded by knocking around Johnson.

The Pirates sent out the 28-year-old lefty — who was pitching in an independent league two years ago after washing out in the Boston Red Sox system — after deciding Locke could use a breather. A surprise All-Star after an 8-2 first half, Locke is 1-2 with a 6.88 ERA in the second half, and Hurdle thought a few days off would allow Locke to work on his mechanics and get some rest.

Locke won't pitch again until next weekend at the earliest. If Pittsburgh decides he needs even more time off, it will likely have to look to someone other than Johnson.

The Pirates, whose 79 wins are tied for the franchise's high-water mark since 1992, made two bold moves last week in hopes of drawing ahead. They brought in Byrd and Buck from the Mets on Tuesday, then made an even bigger splash Saturday when they convinced Morneau to leave Minnesota after 11 seasons.

Morneau arrived at PNC Park midway through Saturday night's blowout and watched the remainder of the game from the dugout. He got a better view on Sunday, playing first base and batting sixth.

The 2006 AL MVP grounded out in his first plate appearance, walked in his second and then lined a single to right field his third time up. He ended his first game for Pittsburgh with a deep fly to the warning track in the ninth.

NOTES: Pittsburgh LHP Wandy Rodriguez is dealing with arthritis in his pitching arm. Rodriguez, who has been on the disabled list since July with forearm tightness, is expected to resume his throwing program this week after a visit with Dr. James Andrews revealed no structural damage to the arm. Pirates general manager Neal Huntington said the team remains hopeful Rodriguez can return in some capacity down the stretch. ... The Pirates begin a three-game series in Milwaukee on Monday. Charlie Morton (6-3, 2.14 ERA) faces Tyler Thornburg (1-0, 1.94). ... St. Louis travels to Cincinnati on Monday to begin a four-game set with the Reds. Adam Wainwright (15-8, 2.96) starts for the Cardinals against Mat Latos (13-5, 3.03).