NEW YORK -- Washington Nationals left-hander Gio Gonzalez strolled through a familiar store to find a pretty good birthday gift for his mother and his manager Thursday night.

Gonzalez continued his domination of the New York Mets at Citi Field by tossing seven strong innings as the Nationals cruised to an 8-3 win in the opener of a four-game series.

Gonzalez (6-1 this season) allowed two runs on five hits and no walks while striking out five as he improved to 13-5 with a 2.94 ERA in 22 career starts against the Mets, including 10-1 with a 1.69 ERA in 15 starts at Citi Field.

The 31-year-old twirled his latest gem in New York on the day his mother and Nationals manager Dusty Baker each celebrated birthdays.

"Happy birthday to Dusty -- you've got to do your best to not lose on his day, especially a man who's seen so many games," Gonzalez said of the 68-year-old Baker, who reached the majors as a player in 1968 and has managed 3,404 regular season games with four teams. "And I also want to send a special happy birthday to my mother. She watched.

"So, I love you, Mom. Happy birthday."

Baker said before the game he's not used to managing a victory on his birthday. Told afterward his teams are now 8-12 when he blows out the candles, Baker grinned.

"I told you," Baker said. "You're aware of (stuff) like that."

Asked if he likes faring well on his birthday, Baker grinned again.

"Heck yeah," Baker said. "Heck yeah. I tried to hit a home run and win on my birthday and Father's Day and Mother's Day. You try to find different ways to get motivated. And those are big days."

Gonzalez wasn't the only one thriving in a road venue that feels like home Thursday. Second baseman Daniel Murphy, who played for the Mets from 2008 through 2015 before signing with the Nationals in January 2016, continued to mash against his former club by going 3-for-5 with a two-run triple during Washington's five-run fifth.

Murphy is batting .394 with eight homers and 28 RBIs in 26 games against the Mets. As Murphy has said since last season, he insisted he has no idea why he is so successful against his ex-franchise, which did not try to re-sign him even after he hit .327 with seven homers during the Mets' World Series run in October and November 2015.

"I would try to replicate it in other places," Murphy said.

And if Murphy is fueled by proving the Mets made a mistake?

"I hope he's fueled the rest of his career, you know what I mean?" Baker said. "They boo him. But it wasn't his fault (he didn't re-sign). But hey, I'm glad we got him."

The Nationals took a lead they'd never relinquish in the first, when Bryce Harper smoked a line drive solo homer to right. Gonzalez laced an RBI single in the fourth before the Mets closed to within 2-1 on Jay Bruce's run-scoring double in the bottom of the inning.

The Nationals broke the game open in the fifth, when they sent eight batters to the plate against Mets right-hander Robert Gsellman (5-4). Anthony Rendon followed Murphy's hit with an RBI single and Michael Taylor hit a two-run homer two batters later.

Brian Goodwin added an RBI double in the sixth for the Nationals (40-26), who won for only the second time in the last seven games to extend their National League East lead over the second-place Mets (30-35) to 9 1/2 games. Rendon and Goodwin had two hits apiece.

Rene Rivera (fifth inning) and Wilmer Flores (eighth inning) hit solo homers for the injury-wracked Mets. who absorbed another blow when Juan Lagares left in the fifth inning with a broken left thumb suffered when he dove for Rendon's hit.

The Mets announced before the game that Neil Walker (left hamstring) and Matt Harvey (right shoulder), both of whom were injured in Wednesday's 9-4 win over the Chicago Cubs, would miss several weeks.

"How many can we possibly continue to have to play through?" Mets manager Terry Collins said. "You know what the answer is? As many as pop up. That's how many you've got to play through."

T.J. Rivera had two hits for the Mets.

Gsellman allowed seven runs on 11 hits and two walks and three strikeouts over five innings.

NOTES: To replace 2B Neil Walker (torn left hamstring), who was placed on the 10-day disabled list, the Mets recalled INF Gavin Cecchini from Triple-A Las Vegas. ... The Mets are expected to officially place RHP Matt Harvey (right scapula bone) on the disabled list Friday. ... The Nationals recalled LHP Matt Grace from Triple-A Syracuse and optioned RHP Trevor Gott to the same affiliate. ... Nationals RF Bryce Harper has 17 homers against the Mets, the fifth-most of any active player. Harper doesn't turn 25 until October.