ST. LOUIS -- Bryce Harper wasn't interested in a pitchers' duel between future All-Star teammates.

Clouting two-run homers in his first two at-bats against St. Louis Cardinals ace Carlos Martinez, the Nationals right fielder gave his team four quick runs and essentially decided Washington's 7-2 win Sunday night at Busch Stadium.

Both homers were off changeups. Harper ripped a 1-2 offering 393 feet into the bleachers in right with Brian Goodwin aboard in the first, then lined an 0-2 pitch at approximately shin level 392 feet to right-center for his 20th homer of the year with Michael A. Taylor aboard in the third.

It was the 13th multi-homer game in Harper's career. He could have had a third had he achieved a bit more elevation on a 110 mph liner off his bat that started the ninth. The ball instead hit off center fielder Tommy Pham's glove on the warning track, and Harper settled for a double.

"Martinez is really good," Harper said. "He's an All-Star. You put the bat on the ball and hope he'll supply a bit of the power, and we were able to do it."

While Washington roughed up Martinez (6-7) for seven hits and five runs over five innings, St. Louis didn't come close to cracking the code on potential National League All-Star starting pitcher Max Scherzer.

In seven scoreless innings, Scherzer (10-5) allowed only two hits, singles by Greg Garcia in the first and pinch hitter Luke Voit in the fifth. Scherzer walked two and fanned 12, giving him 163 strikeouts in 120 2/3 innings.

Voit's hit was just the 25th by a right-handed batter off Scherzer this year. Scherzer has essentially turned righties into pitchers at the plate, as their average against him is .118.

"Guys like he and (Clayton) Kershaw," said Nationals manager Dusty Baker, referring to the Los Angeles Dodgers' ace left-hander, "this is what they're supposed to do. They're paid handsomely to do it, and they take pride in doing it. They know the team depends on them."

The Nationals (48-34) had lost three in a row entering this one, but it was clear Scherzer wasn't going to let that become four straight. He fanned five of the first six batters he faced and got to 10 before the fifth inning ended.

It was Scherzer's 10th double-figure strikeout game of the year and the 59th of his career.

"This is the majors; you've got to be up every single night," he said when asked if being a stopper gave him extra motivation. "Your job is to go out and pitch deep into the game."

After scoring just one run in each of the series' first two games, the Nationals backed up Baker's words that their offense would erupt before leaving town. Anthony Rendon added an RBI double in the third inning, and Wilmer Difo and Goodwin supplied sacrifice flies in the eighth.

Pham lined a two-run homer to right-center in the eighth for the Cardinals, who saw a four-game winning streak end and lost for only the second time in eight games.

Martinez, who walked four and whiffed three, failed to log a quality start for just the fifth time in 17 outings.

"Every type of pitch I would throw, they (made) excellent contact," he said through an interpreter. "So I have to give credit to them for that."

Washington maintained a 7 1/2-game lead in the NL East on the Atlanta Braves. St. Louis (39-42) remains in third place in the NL Central, 3 1/2 games behind the first-place Milwaukee Brewers.

NOTES: Washington 1B Ryan Zimmerman, 2B Daniel Murphy and RF Bryce Harper were chosen starters for the NL All-Star team, which also will include RHPs Max Scherzer and Stephen Strasburg. C Yadier Molina and RHP Carlos Martinez will represent the Cardinals. ... St. Louis made a pair of minor league trades Sunday based around international cap space. The Cardinals acquired INFs Stanley Espinal and Imeldo Diaz from Boston for cap considerations, then got OF Lane Thomas from Toronto for cap space. ... A ninth-inning run Saturday night allowed the Nationals to remain the only National League team not to be shut out this year. ... The Cardinals signed fourth-round draft pick Kramer Robertson, a shortstop from LSU. Robertson scored a Division I-high 83 runs for the Tigers, who reached the championship round of the College World Series before being bounced by Florida.