Now they're counting on him to make sure they maintain first place, starting Jordan Zimmermann on Friday night against a Philadelphia Phillies club at the bottom of the East but coming home after sweeping a division leader.A big reason Zimmermann is headed to next week's Midsummer Classic at Target Field, a few hours from his hometown of Auburndale, Wisconsin, is that he's rediscovered an effective slider. He credits that pitch for his dominance since the beginning of June, posting a 1.26 ERA in seven starts with seven walks and 46 strikeouts over 50 innings."Five weeks ago, I was thinking I would be on vacation (for the All-Star break)," Zimmermann told MLB's official website. "I just started throwing strikes and locating better. The slider finally came back. I didn't have it for a month and a half. I was able to get that back. That's a big pitch."A 19-game winner last year, Zimmermann (6-4, 2.79 ERA) has virtually no shot of reaching his 2013 victory total mainly because Washington has provided him no more than one run of support in half of his 18 starts. That's happened in four of his last five outings as he's gone 1-2, and he didn't get a decision Sunday when he threw six scoreless innings in a 2-1 victory over the Chicago Cubs.His recent run of brilliance began against the Phillies, going eight innings in a 7-0 victory June 3. Zimmermann is 4-1 with a 2.04 ERA in his last five starts against them.The right-hander now looks to help the Nationals (49-41) bounce back from their first series loss since mid-June. They dropped two of three in a rain-shortened series against Baltimore, including a 4-3 defeat Thursday that cut their division lead to a percentage point over Atlanta.The Phillies (41-51) are nine games back but riding high, sweeping four games at NL-best Milwaukee this week. They totaled 25 runs in the series and batted .435 with runners in scoring position over the final three games, compared to .149 in the previous 11."It's crazy," shortstop Jimmy Rollins said of the sweep, which came after Philadelphia lost nine of 10. "You can't explain it. You just hope it's good-crazy and not bad-crazy. We've been a lot of bad-crazy."The Phillies, coming off a 5-5 road trip, are tied for baseball's second-worst home record (18-26) and suffered a four-game sweep to Atlanta in their last series at Citizens Bank Park.A.J. Burnett (5-8, 3.92) is seeking a seventh consecutive quality start, but the Phillies have lost his last three as he's gone 0-2 despite 25 strikeouts in 20 innings.Burnett was 5-0 with a 1.82 ERA in his previous nine starts against the Nationals before being ripped by them on June 4, allowing eight runs in six innings of an 8-4 loss at Washington.Jayson Werth's only two hits in 20 at-bats against Burnett are home runs. The former Phillie has gone deep each of the last two days and is batting .400 this month with four homers and 12 RBIs in eight games.Anthony Rendon is 3 for 7 with a homer off Burnett this year and had his third multihit effort in five games Thursday, hours after learning he didn't win the fan vote for the NL's last All-Star spot.Wilson Ramos is riding a career-best, 13-game hitting streak, but Bryce Harper is in a 1-for-20 slump.Shortstop Ian Desmond, meanwhile, is uncertain to play Friday after leaving Thursday's game when he was hit by a pitch in the right thumb.Phillies slugger Ryan Howard halted a 20-game homerless drought and a 4-for-44 slump Thursday as he went 2 for 5 with three RBIs.