PHILADELPHIA — Ever since Philadelphia general manager Ruben Amaro Jr. called his team's offense "poor" and predicted changes, the Phillies haven't lost.

Jimmy Rollins homered twice and A.J. Burnett pitched 7 2-3 strong innings to lead the Phillies to their fifth straight victory, 6-2 over the Washington Nationals on Friday night.

Domonic Brown doubled and drove in two runs for Philadelphia, which matched its longest winning streak of the season.

It has been a surprising run for the Phillies, who had lost 13 of 16 before a four-game sweep of the NL Central-leading Brewers in Milwaukee.

The Phillies have averaged 6.2 runs per game during their winning string.

"I know the hitters had a good meeting about where we were and adjustments that needed to be made," manager Ryne Sandberg said. "Key guys seemed to come up big in situations right from that point on and it's been different guys each day. That's what it takes. Now it feels like the whole lineup is chipping in and doing their part."

Said Rollins: "There's something going on and hopefully it turns into a fire."

Bryce Harper homered for the Nationals, who have lost three of four.

Washington right-hander Jordan Zimmermann (6-5) abruptly left his start in the fourth inning with a right biceps injury.

Zimmermann, scheduled to participate in his second straight All-Star Game on Tuesday, will be evaluated further on Saturday. He isn't expected to pitch on Tuesday, according to manager Matt Williams.

Burnett (6-8) allowed two runs and five hits while striking out six and walking four.

"We're playing good ball," Burnett said. "It's good to see this team clicking on all cylinders."

As with the rest of the starters, Burnett has been a victim of lack of run support this season.

"You go about your business the same, but it's definitely better to get some runs," he said.

Zimmermann, who had Tommy John surgery in August 2009, called the Nationals' training staff out after throwing a pitch to Cameron Rupp with one out in the fourth inning. He showed no obvious discomfort, but left the mound after a short discussion with the training staff and Williams.

Zimmermann doesn't feel the problem is related to his shoulder or elbow.

"It was gradually getting worse with every pitch," he said. "I knew something wasn't right. I didn't want to push it too far."

He said not pitching in the All-Star Game would be a disappointment.

"Obviously, you want to go," he said. "I had all my plans made and I wanted to pitch in front of my family. But the main thing is to get healthy."

Zimmermann left after allowing four runs and six hits. He threw 53 pitches, 36 for strikes.

Zimmermann has a 1.26 ERA since June 1 with 46 strikeouts and seven walks in 50 innings over seven starts. But he gave up four runs and six hits in 3 1-3 innings against the Phillies.

Brown gave Philadelphia the lead with a two-run double in the second and the first of Rollins' homers, a two-run shot to right, put Philadelphia in front 4-0.

Rupp's RBI double off Craig Stammen in the sixth put Philadelphia ahead 5-0 before Harper broke out of a 1-for-22 slump by leading off the seventh with a homer to deep right to pull Washington within 5-1. It was just the second homer of the season for Harper, who missed 57 games due to a thumb injury.

Rollins got the run back in the bottom of the inning, just clearing the wall in right for his ninth career multi-homer game.

Batting leadoff and playing center field, Grady Sizemore went 1 for 4 with a single in his first game with the Phillies after being called up from Triple-A Lehigh Valley. The three-time All-Star whose career was derailed by injuries had been released by the Red Sox last month after batting .216 with two homers and 15 RBIs in 52 games. The 31-year-old missed all of the 2012 and 2013 seasons due to an assortment of injuries.

After leaving Thursday's game at Baltimore after getting hit by a pitch on his right thumb, Washington's Ian Desmond didn't play Friday. Desmond entered Friday leading all shortstops in the majors with 55 RBIs.

NOTES: Philadelphia improved to 19-27 at Citizens Bank Park, where they have struggled this season. ... Rollins last hit two homers in a game on Aug. 1, 2012, at Washington. . Washington's Wilson Ramos extended his hitting streak to 14 games with a fifth-inning single. . The Phillies also won five straight from June 16-20 at Atlanta and St. Louis. . Nationals RHP Stephen Strasburg (7-6, 3.47) opposes Phillies LHP Cole Hamels (3-5, 2.87) Saturday night.