WASHINGTON -- Anthony Rendon did some homework before facing Seattle Mariners right-hander Christian Bergman.

"I was watching him on video before the game," the Washington Nationals third baseman said. "He was hitting his spots."

That was certainly not the case Tuesday, as Bergman gave up 14 hits and 10 runs in four innings as the Nationals crushed the Mariners 10-1. Washington scored eight runs in the fourth inning, collecting six hits in a row at one point.

Rendon went 3-for-4 with two homers, a double and five RBIs, and right-hander Joe Ross came up from Triple-A to allow one run in eight innings for the win.

"He has been working hard all season," Rendon said of Ross. "He has gotten some bad breaks."

Ross (2-0) entered the game with a 7.47 ERA in the majors this year, but he lowered the mark to 5.32. He made three starts earlier this month in the minors.

Ross allowed just five hits and struck out six with no walks while matching the longest outing of his career.

"It was very important," Washington manager Dusty Baker said of Ross giving his bullpen a breather. "He didn't want to come out.

"That is the guy that we know. Joe was pitching with confidence and conviction. Those runs didn't hurt."

Ross has been given 62 runs of support this year, the most in major league history for any pitcher in his first four starts of a season.

"I guess we were swinging at good pitches," Rendon said.

Jayson Werth and Bryce Harper also homered for the Nationals, who got at least one hit from every starter.

Seattle's Mike Zunino, just called up from Triple-A Tacoma, hit a solo homer off Ross in the sixth after Washington built a 10-1 lead.

Ryan Zimmerman had three hits for Washington, and Trea Turner and Michael A. Taylor added two each.

Jean Segura and Kyle Seager had two hits apiece for Seattle. Bergman (1-2) walked two and didn't record a strikeout.

"There were a couple of opportunities to get out of there with minimal damage just couldn't quite get that last guy. So that's unfortunately what happens," Servais said of the big fourth.

In the first game of the interleague series, Washington improved to 27-17 while Seattle fell to 20-26 with its fourth loss in a row. Matt Grace pitched the ninth for Washington.

The Nationals broke the game open in the fourth after Rendon hit a two-run homer in the second. Rendon hit two homers off starter Bergman, and Werth and Harper also went deep against the beleaguered hurler, whose ERA jumped from 2.25 to 6.30.

"Kind of unraveled on us. We had some chances to get out of the inning and they just got on a hit parade and we couldn't stop it," Seattle manager Scott Servais said.

Rendon hit his sixth homer of the year with one out in the second to give the Nationals a 2-0 lead. His homer also scored Zimmerman, who led off with a single as a light rain fell at Nationals Park.

The field got very wet after three innings and Robinson Cano, who just came off the disabled list, just jogged to first base when he grounded out to short to end the top of the fourth.

The Nationals amassed a team-record nine hits in the fourth. Matt Wieters had an RBI single, Turner drove in a run with a triple, Werth hit a two-run homer, Harper followed with a solo shot and Rendon hit a three-run homer to make it 10-0. Rendon had three homers and 10 RBIs at home against the New York Mets on April 30.

"Just kind of how we're losing and not really in the game that makes it a little bit tough," Servais said. "We knew we were going to get in this tough stretch here with the state of our starting pitching influx and trying to run a lot of inexperienced guys out there; it's going to happen."

NOTES: Seattle 2B Robinson Cano (right quad strain) came off the 10-day disabled list before the game, and he went 0-for-3. The Mariners had already cleared a roster spot for him with a flurry of moves Monday. ... Washington RHP Joe Ross, promoted from Triple-A Syracuse, made his first major league start since April 30, when he gave up five runs to the New York Mets. Nationals OF Brian Goodwin was sent to Syracuse to make room for Ross on the roster. ... Seattle made its first visit to Washington since 2011. The Mariners are now 0-7 all-time in the nation's capital. ... Washington RHP Tanner Roark (3-2, 4.73) will face Seattle RHP Sam Gaviglio (0-0, 1.29) on Wednesday.