(SportsNetwork.com) - The Washington Nationals take aim at another series victory on Monday afternoon when they visit Wrigley Field to take on the Chicago Cubs in the opener of a three-game series.

Washington has won seven of eight to open a 2 1/2-game lead over the New York Mets in the National League East. The division-leading Nationals left Philadelphia with a series-clinching, 4-1 victory on Sunday. Bryce Harper stayed hot with a pair of RBI and Gio Gonzalez worked 6 1/3 innings of one-run ball, striking out seven and walking one.

"Being able to get the W was huge," Harper said. "What we did (Sunday) to get that W -- going on the road right now -- I'm just glad we ended it on a good note in this homestand."

The Nats will head to Cincinnati following this series.

"We've been aware that we have a tough schedule coming up," Cubs pitcher Jake Arrieta said. "We approach games with equal importance regardless of who the opponent is. At the end of the day, every one counts. We've seen several times how seasons can come down to the final four, five days determining who gets in and who goes home. "We're going to value these games just like any other, but it's kind of a measuring stick."

Chicago returns home after dropping two of three in Arizona over the weekend. The Cubs are coming off Sunday's 4-3 setback, in which they managed only five hits and committed a pair of errors. Jason Hammel struck out nine batters over seven innings but allowed four runs to drop to 3-2 on the season.

Miguel Montero hit a solo home run in the second inning against his former team, which traded him to Chicago for two minor league pitchers.

"There's no hard feelings," Montero said. "(Going yard) definitely was a good feeling."

Tsuyoshi Wada will toe the rubber for Chicago on Monday afternoon. After battling a left groin strain in the spring, the southpaw made his season debut in San Diego on Wednesday and struck out a career-high nine batters in only 4 2/3 innings. Wada allowed two runs on four hits and issued just one walk, with his day coming to an end after 69 pitches.

For Washington, Tanner Roark steps into injured starter Doug Fister's spot in the rotation and will make his first start since last September. The right- hander has spent all of 2015 in the bullpen to this point after making 31 starts last season.

Roark was 0-2 with a 5.54 ERA in two starts against the Cubs in 2014.

This is the first of seven meetings between these two teams over the next two weeks.