SAN FRANCISCO -- After a 4-5 road trip, the Giants returned to Oracle Park on Monday night to open a crucial homestand against the Nationals and the Phillies, two of the teams they’re chasing in the National League Wild Card race.

It didn’t begin on the best note.

The Giants fell flat in a 4-0 shutout loss against the Nationals to slip below .500 for the first time since July 20. While a scorching 17-3 stretch thrust the Giants into contention, they’ve begun to lose steam at a pivotal stretch of their schedule, dropping seven of their last 11 games to fall to 56-57 and 3 1/2 games out of the NL Wild Card picture.

• Box score

“Obviously, you know how seasons go,” right-hander Jeff Samardzija said. “To stay that hot for three months would be a pretty remarkable thing. We just need to keep our heads on straight and keep coming to the park every day.

“We came off a long road trip, and this is our first day back. We’ll get back out there tomorrow and play hard. It’s a good team we’re playing against. Tomorrow is a big game for us.”

Samardzija, who finished July 4-1 with a 2.09 ERA, needed 98 pitches to get through four innings while allowing one run, walking three and striking out three. His line likely would have looked worse were it not for center fielder Kevin Pillar, who made a brilliant diving catch to rob Kurt Suzuki of extra bases and keep the Nationals off the board in the second inning.

Washington scored its lone run off Samardzija on an RBI single from Anthony Rendon in the third.

“Outside of just battling and fighting, there wasn’t too much positive out there for me,” Samardzija said. “They made me work. Slider wasn’t very good today. They fouled off a lot of pitches. Everything was kind of the same speed, so the pitch count got a little high. That was the story.”

Samardzija was replaced by rookie reliever Sam Coonrod, who issued three walks to load the bases and then balked in a run in the fifth. The Nationals expanded their lead after Pillar appeared to lose Matt Adams’ fly ball in the twilight, allowing it to fall for an RBI double that made it 3-0.

A suddenly flagging Giants offense, which is without one of its best hitters after losing Alex Dickerson to a right oblique strain, couldn’t overcome the deficit. After averaging 6.8 runs per game over their magical July run, the Giants appear to have reverted to their early season woes, averaging only 2.9 runs per game over their last 11 contests.

They produced only seven hits on Monday, six of which were singles. Samardzija delivered the Giants’ lone extra-base hit of the night, doubling off Nationals right-hander Erick Fedde in the third.

“We felt good going into the game, but we just couldn’t get things going,” manager Bruce Bochy said. “That’s all. You hit a couple balls hard. You hope that gets us going, but the balls were right at them tonight. It was a tough night for our hitters.”

The Giants watched the red-hot Mets move past them in the standings and could be in danger of losing more ground if their rough start to August continues. While there are still almost two months left in this season, Samardzija recognized the need to approach this week’s games with a greater sense of urgency.

“I think with it being those two teams and where they’re at, obviously, it puts a little more importance on it,” Samardzija said. “Regardless of what happens this week, there’s still a lot of baseball to be played. No matter how it turns out, either way, it doesn’t really matter because you still need to keep playing for another month and a half.

“Obviously, there’s importance on it because they’re good teams and they’re teams we’re chasing, but that’s really about where it stops just because you know there’s still work to be done after they leave.”