New York at Washington

The Washington Nationals' lead in the NL East is shrinking due to an inconsistent stretch.

Unfortunately for the New York Mets, they're not the team closing the gap.

The Nationals begin a key 10-game stretch against their two closest pursuers in the division Tuesday night when they host the sliding Mets in the opener of a three-game set.

Washington (51-36) has alternated wins and losses in its last eight games, concluding a four-game split at Miami with a 5-3 loss Monday.

Since July 5, the Nationals' lead in the East has slipped from 4 1/2 games over New York to 2 1/2 ahead of second-place Atlanta, which has won seven in a row. The Mets (46-43) are third and trail Washington by six games after losing four straight, including three to the Braves over the weekend.

"We knew coming into here that every game is important, especially coming into Atlanta and then (going to) Washington," said Johan Santana, the losing pitcher in Sunday's 6-1 defeat. "If we compete, we're right there. It's tough."

Washington is hoping to create some separation. After this series, the Nationals play a four-game home set against the Braves before visiting the Mets for three more meetings.

A red-hot Ryan Zimmerman should help. The third baseman is hitting .373 with seven homers and 21 RBIs in his last 18 games, going 8 for 15 with a pair of homers in the last four and coming a triple shy of the cycle Monday.

He's batting .329 in his last 18 meetings with New York, and is 4 for 8 against Tuesday's scheduled starter Jonathon Niese.

Niese (7-4, 3.73) is getting his first start against the Nationals this season. He's 2-0 with a 3.42 ERA and 24 strikeouts in 23 2-3 innings over four career starts versus Washington.

The left-hander was hit hard in his latest outing July 8, surrendering four runs in the opening inning and three more in the seventh in a 7-0 loss to the Chicago Cubs. That was in stark contrast with his previous six outings, in which he went 4-1 with a 1.74 ERA.

The Nationals will turn to Ross Detwiler (4-3, 3.43), who has no record and a 3.78 ERA in three starts since returning to the rotation in place of Chien-Ming Wang. The left-hander wasn't very sharp in his most recent start July 5, allowing three runs and 11 hits in five innings before his teammates rallied for a 6-5 win over San Francisco.

Detwiler is 3-1 with a 3.60 ERA in seven games - four starts - against the Mets, beating them twice this year. One of those outings was his season debut April 10, when he fanned six in five scoreless innings during a 6-2 victory in New York.

The Mets may have Jason Bay back from the disabled list Tuesday. A concussion has kept him out since June 15, and he's played in only seven games since April.

The outfielder went 3 for 16 with six walks during his latest rehab stint in the minors. He's batting .187 with four homers in 22 games for New York.

Bay's possible return may be timely if Lucas Duda is out of the lineup for a third game in a row with an injured left hamstring. Duda is 6 for 19 with three homers and six RBIs in his last six games at Washington.