Rookie right-hander Joe Kelly tries to maintain his team's hold on a playoff spot Monday afternoon when the St. Louis Cardinals host the New York Mets in the first of three straight games at Busch Stadium.

The Cardinals enter the series with a half-game lead over Los Angeles for the second of two National League wild card playoff berths, with the Pittsburgh Pirates 1 1/2 games off the pace.

St. Louis, which made the postseason as a wild card last year and wound up with a World Series title, trails first-place Cincinnati by 9 1/2 games in the National League's Central Division.

The Mets, who are tied with Philadelphia for third in the NL's East Division, are eight games off the wild card pace.

Kelly, a third-round pick of the Cardinals in 2009, makes his first major- league appearance against New York while starting for the 14th time.

He fell to 4-6 overall in his most recent outing on Aug. 29 after allowing eight hits and five runs in five innings of a 5-0 defeat at Pittsburgh.

Previously, he'd earned a relief win with three innings of one-run ball in an Aug. 24 victory at Cincinnati.

His last win as a starter came on Aug. 14 against Arizona.

In nine appearances - eight starts - at home in 2012, he's 2-3 with a 3.06 earned run average.

New York opposes him with fellow rookie Collin McHugh, a Naperville, Ill. native who makes his second big-league appearance.

The 25-year-old was stellar in his initial trip to a major-league mound, tossing seven innings of scoreless two-hit ball with nine strikeouts while earning a no-decision in the Mets' 1-0 loss to Colorado on Aug. 23.

"It was trying to contain the nerves," McHugh said. "A lot of people gave some really good advice and said you're going to be nervous. It's a fact. Just contain those and go out and do your thing."

McHugh has split minor-league time at Double-A Binghamton and Triple-A Buffalo this season, combining to go 7-9 with a 2.91 ERA across 148 1/3 innings while allowing 123 hits and striking out 135.

On Sunday in Miami, Jason Bay broke out of a 10-for-83 slump and delivered two hits, including a first-inning grand slam to help the Mets down the Marlins, 5-1, and complete a three-game sweep.

The Mets, winners in seven of their last eight games, swept the Marlins for the second time this season.

Chris Young (4-7) started for the Mets and pitched five innings. He struck out three and allowed just one run on five hits.

In Washington, Danny Espinosa's RBI single during a two-run seventh inning proved to be the difference as the Nationals escaped with a 4-3 win over the Cardinals in the finale of a four-game series.

Lance Lynn (13-6) took the loss after surrendering two runs on four hits in the seventh inning. Daniel Descalso smacked a two-run home run and Tony Cruz added an RBI double for the defending World Series champs, who lost three of four in this series.

The teams have split season series in 2010 and 2011, with the Cardinals last winning, five games to four, in 2009. New York won three of four games in 2012 when the teams played at Citi Field from June 1-4.