Jason Hammel looks to continue his mastery of the Washington Nationals when the improving Chicago Cubs visit Friday to start a three-game series. Hammel is 7-0 with a 3.12 ERA in nine career starts against the Nationals, including a 7-2 victory last Friday to help the Cubs gain a split of the four-game home set. Chicago comes in off three consecutive wins at Boston while Washington has won five straight, moving within a half-game of first-place Atlanta in the National League East.All-Star Bryce Harper returned from two months on the disabled list to hit safely in all three games as the Nationals swept Colorado earlier in the week. Ian Desmond, who leads Washington is homers (15) and RBIs (51), knocked in five runs during that series and the Nationals have surrendered only nine runs during their win streak. Starlin Castro is 7-for-16 over the last four contests for the Cubs, who are 5-2 in their last seven overall.TV: 11:05 a.m. ET; MLB Network, WGN (Chicago), MASN, WUSA 9 (Washington)PITCHING MATCHUP: Cubs RH Jason Hammel (7-5, 2.98 ERA) vs. Nationals RH Tanner Roark (7-5, 2.98)Hammel snapped a four-game winless streak by giving up two runs on five hits and striking out six over 6 1/3 innings to beat the Nationals. The 31-year-old South Carolina native has allowed three or fewer runs in 13 of his 16 starts, but is 3-4 on the road this season. Ryan Zimmerman is 10-for-28 with a homer against Hammel, who has won four decisions with a 3.21 ERA at Nationals Park.Roark saw his four-game win streak come to an end against Hammel and the Cubs in his last start Friday, giving up four runs over six innings. That outing was only the second in his last 10 that he has permitted more than two runs while improving to 14-6 in his first two seasons. Chris Coghlan is 3-for-6 versus Roark, who has yielded six runs in 7 2/3 innings against the Cubs in his career.WALK-OFFS1. Chicago has won four straight on the road for the first time since September 2012 and is 6-1 in its last seven away from home. 2. Washington 2B-3B Anthony Rendon owns a seven-game hitting streak overall and is 7-for-16 against the Cubs this season.3. The Cubs are only 24-20 when their pitching staff has produced a quality start this season.PREDICTION: Cubs 5, Nationals 3