WASHINGTON -- The Washington Nationals have ranked among the league leaders most of this season in team ERA and fielding percentage.

But Nationals manager Dusty Baker is still not satisfied as his club begins a three-game series at home Friday against the San Francisco Giants in a matchup of first-place teams.

While his club leads the league in homers, Baker would like to see his team hit better for average and especially when runners are in scoring position.

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"I don't like being in the middle of the pack on offense, I will tell you that," Baker told reporters during a road series this week in Arizona. "This is the offensive time of the year, August and September."

The Nationals (64-44), who had Thursday off, flexed their offensive muscle by beating Arizona 14-1 on Monday, 10-4 on Tuesday and 8-3 on Wednesday.

"We were able to get the series sweep with an off day (Thursday)," infielder Daniel Murphy said Wednesday on the Mid-Atlantic Sports Network.

The Giants wrapped up a series at Philadelphia on Thursday afternoon with a 3-2 victory in 10 innings while the Nationals ended a three-city road trip by going 6-3 in Cleveland, San Francisco and Arizona. Washington outscored foes 54-27 on the trip.

San Francisco (62-46) had the worst mark in the majors at 4-13 since the All-Star break going into Thursday's play.

"It's hard to believe," Giants right-hander Johnny Cueto told MLB.com. "We're a good team. All we can do is keep grinding and putting our best stuff out there every time."

Bryce Harper had the flu and missed Tuesday's game in Arizona. "He looks a lot better," Baker said of Harper, who was back in the starting lineup Wednesday.

The Giants are slated to start right-hander Jeff Samardzija, who is 7-16 with a 4.92 ERA in 57 games (25 starts) in the month of August.

He was slated to start for Thursday but was pushed back when Matt Moore, acquired in a trade from Tampa Bay on Monday, pitched against the Phillies.

Samardzija (9-7, 4.30 this season) has some history with several Washington hitters.

Murphy, the Player of the Month for July in the National League, is hitting .500 in 12 at-bats with one homer against the former Notre Dame football player. Washington catcher Wilson Ramos is hitting .364 with two homers in 11 at-bats against him. Murphy and Ramos went deep in the series at Arizona.

Harper is hitting .200 in 10 at-bats against Samardzija and Ben Revere is at .333 in nine trips.

Harper enters Friday with an average of .130 in his last seven games, .115 in his last 15 and .194 in his last 30.

"Sooner or later Harper will really bust out of this," Baker said.

Washington infielder Danny Espinosa, who was on fire in June, is hitting .115 in his last 15 games and .196 in his last 30.

Washington has a new closer -- Mark Melancon -- since it last played at Nationals Park.

Jonathan Papelbon, acquired last year at the trade deadline, lost the role after Melancon was acquired in a deal with the Pittsburgh Pirates on Saturday for reliever Felipe Rivero and a minor league pitcher.

The Washington Post reported Thursday that left-hander Gio Gonzalez (6-9, 4.29) would make the start on regular rest Friday against the Giants. That will allow the Nationals to skip over the fifth man in the rotation, which has been rookies Lucas Giolito and Reynaldo Lopez in the past few weeks.

Hunter Pence is 1-for-17 against Gonzalez while Buster Posey is 5-for-15.