WASHINGTON -- When the Nationals and Giants met last weekend in San Francisco, neither Stephen Strasburg or Madison Bumgarner pitched in the four-game series.

It almost happened this time as the two All-Stars were originally slated to face each other Sunday. But the Nationals made a pitching change and will go with Tanner Roark on Sunday after Strasburg went Saturday against the Giants and suffered the 7-1 loss.

"It was a big game," said manager Bruce Bochy, whose club had lost 14 of its previous 19 outings.

The Giants got a lift Saturday from third baseman Eduardo Nunez, who came to the team in a trade in late July. He had four hits Saturday, including two triples.

"You saw what he could do tonight. You saw what he could do tonight. He brings a lot of energy to the lineup," Bochy said of Nunez. "He can do a lot of things for you. I knew I was going to play him today. It is important to get him going. This year he came into his own and made the All-Star team. This kid is talented. He adds a dimension with speed and energy he brings to the club."

The Giants try to gain some momentum with Bumgarner (10-6, 2.25 ERA), who has made 23 starts this year and averages nearly seven innings per outing. He has gone 155 2/3 innings and allowed 122 hits and 38 walks with 174 strikeouts. Opponents are hitting just .211 against him.

While Bumgarner is a former World Series MVP, Roark may be one of the most underrated starters in the game.

Roark, a 25th-round pick by the Texas Rangers, became a starter for the Nationals in 2014 and won 15 games.

He was used mostly out of the bullpen last year but has been in the rotation again this year.

The University of Illinois product is 11-6 with a 3.02 ERA in 23 games (22 starts). He has gone 143 innings and allowed 125 hits and 43 walks with 119 strikeouts. Opponents have an average of .239 against Roark.

He had a career-high 15 strikeouts against the Twins on April 23.

"I was just locked in. Every single pitch was on point," Roark said in the team's Inside Pitch magazine.

Giants hitters have very little track record against Roark. Buster Posey is 4-for-9 against Roark while Brandon Crawford is 2-for-7.

Bumgarner is 0-1 in his last three starts while Roark is 2-1 with a 4.42 ERA in that span.

Roark is 4-0 with a 3.32 ERA in five games (two starts) against the Giants. He faced them on July 28 and gave up just one run in seven innings. Roark leads the league in outings in which he has allowed no runs while going seven innings, which he has done six times.

While the Nationals only face the Giants in two series per year, Washington batters have fared well against North Carolina native Bumgarner in a small sample size.

Anthony Rendon is hitting .444 in nine at-bats and Ben Revere is 7-for-14.

Clint Robinson, a backup first baseman, has hit .667 in three at-bats against Bumgarner.

The availability of right fielder Bryce Harper may be in question Sunday for Washington.

He grimaced while fouling off a pitch in his second at-bat Saturday night. He stayed in the game but struck out for the third time in three trips to the plate before he was replaced in right field by Brian Goodwin.

"He's OK. He's had a stiff neck for a couple of days," Washington manager Dusty Baker said. "Anybody who has ever had a stiff neck, I mean, you know you're not yourself. So I took him out for precaution. We'll see if it's any better tomorrow.

"You can wake up in the morning and it's an issue. He's been dealing with this for a couple of days. I think this was the second day. I decided to take him out of the game."

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