The Mariners have now won 17 of their last 20 home games and are 30-19 since the All-Star break, tied for the second-best mark in the American League in that span. At 66-70 overall, they're one shy of last year's victory total with 26 games still to play.
Vargas has been a key piece of that improvement with a career-best 3.80 ERA as the team's No. 2 starter behind Hernandez, but he'd gone just 4 2/3 and four innings in his previous two starts and had just one victory in August after being named the AL Pitcher of the Month in a 5-0 July.
The 29-year-old got back on track in his Labor Day outing in front of 21,641 fans, allowing just a first-inning run and finishing with five strikeouts and no walks before manager Eric Wedge went to his bullpen in the eighth.
"The last couple starts have been a little rough on him, but he was back to his normal self today, which was good to see," said Wedge. "I probably could have sent him back out for the eighth inning, but with his last couple outings, I felt like that was enough for him.
"I love the fact he wanted to keep going, but he has something good to work off of today. He has further starts ahead of him here in September and I want him to finish strong."
Seattle provided Vargas all the offense he needed with four runs in the fourth, bunching four of their six hits on the day in that frame and taking advantage of a pair of errors and a hit batter by Clay Buchholz as well.
The Red Sox (62-74) have been outscored 58-16 during a seven-game losing streak on their nine-game road trip.
"I think the guys are very mentally and physically tired," said Boston manager Bobby Valentine. "They need the night off here. Come back, will feel like two nights. We got to kick it in, we got to have better at-bats."
Vargas had beaten Boston only once in five previous meetings, but he acknowledged this was a far different lineup, as the Red Sox have gone young after dealing away veterans Adrian Gonzalez, Carl Crawford and Kevin Youkilis and putting David Ortiz on the disabled list.
So Vargas said he followed Miguel Olivo's lead, with the veteran catcher going more to the changeup after Vargas had struggled his past two starts.
"The only guys I'd really seen were [Mike] Aviles, [Cody] Ross, [Dustin] Pedroia and [Jacoby] Ellsbury," Vargas said. "Other than that, it was completely different. So I just let Miggy call it. There's not a whole lot you can do when you haven't seen guys, and it's a day game and you don't really have time for a meeting or to watch video. So you just kind of see what they've got and what you've got and what works."
Boston did its only damage against Vargas in the first, as Pedroia hit a ground-rule double to left-center and scored on a single by Ross.
The Mariners had only one baserunner in the first three innings against Buchholz before they broke through in the fourth, ignited by back-to-back RBI singles by John Jaso and Justin Smoak after Franklin Gutierrez led off with an infield single and Kyle Seager was nicked on the elbow by a pitch.
Jaso then scored the third run of the inning when he tagged at third on a fly ball by Eric Thames and faked going home, then set sail after Ellsbury's throw from shallow center skidded wide of the catcher for an error.
"It seemed like there were some good at-bats and we were able to go first-to-third on some hits," said Jaso. "I think that aggressiveness paid off. A lot of times they say don't make the first out at third base, but that kind of aggressive baserunning keeps a lot of momentum going on the offensive side."
The final run crossed the plate when rookie shortstop Jose Iglesias mishandled a ground ball by Carlos Peguero, double-clutching and losing the ball momentarily when Olivo was bearing down on second base when he first thought about going there to start a double play. Instead, the Sox wound up with nothing.
"You have to string some good at-bats together and they gave us a few extra opportunities, too," Wedge said. "I thought we took advantage of it, and that's what you've got to do. We had a lot of hustle. Jaso goes first-to-third. Olivo's hustle into second base altered that play, just because of how quick he got to second. It never hurts when you're forcing the defense like that."